Installation guide | e Red Hat Enterprise Linux 6 DM Multipath

Red Hat Enterprise Linux 6
DM Multipath
DM Multipath Configuration and Administration
Edition 1
Red Hat Enterprise Linux 6 DM Multipath
DM Multipath Configuration and Administration
Edition 1
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Abstract
This bo o k pro vides info rmatio n o n using the Device-Mapper Multipath feature o f Red Hat
Enterprise Linux 6 .
T able of Cont ent s
T able of Contents
.Preface
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. . . . . . . . . .
⁠1. Aud ienc e
3
⁠2 . Related Do c umentatio n
3
⁠3 . We Need Feed b ac k!
3
⁠4 . Do c ument Co nventio ns
4
⁠4 .1. Typ o g rap hic Co nventio ns
4
⁠4 .2. Pull-q uo te Co nventio ns
5
⁠4 .3. No tes and Warning s
6
. .hapt
⁠C
. . . .er
. .1. .. Device
. . . . . . Mapper
. . . . . . . Mult
. . . . ipat
. . . .hing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7. . . . . . . . . .
⁠1.1. New and Chang ed Features
7
⁠1.1.1. New and Chang ed Features fo r Red Hat Enterp ris e Linux 6 .0
7
⁠1.1.2. New and Chang ed Features fo r Red Hat Enterp ris e Linux 6 .1
8
⁠1.1.3. New and Chang ed Features
⁠1.1.4. New and Chang ed Features
⁠1.1.5. New and Chang ed Features
⁠1.1.6 . New and Chang ed Features
⁠1.1.7. New and Chang ed Features
⁠1.2. O verview o f DM-Multip ath
⁠1.3. Sto rag e Array Sup p o rt
⁠1.4. DM-Multip ath Co mp o nents
⁠1.5. DM-Multip ath Setup O verview
fo r Red
fo r Red
fo r Red
fo r Red
fo r Red
Hat Enterp ris e Linux 6 .2
Hat Enterp ris e Linux 6 .3
Hat Enterp ris e Linux 6 .4
Hat Enterp ris e Linux 6 .5
Hat Enterp ris e Linux 6 .6
8
8
9
9
9
9
12
12
13
. .hapt
⁠C
. . . .er
. .2. .. Mult
. . . . ipat
. . . .h. Devices
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1. 4. . . . . . . . . .
⁠2 .1. Multip ath Devic e Id entifiers
14
⁠2 .2. Co ns is tent Multip ath Devic e Names in a Clus ter
14
⁠2 .3. Multip ath Devic e Attrib utes
15
⁠2 .4. Multip ath Devic es in Lo g ic al Vo lumes
15
. .hapt
⁠C
. . . .er
. .3.
. .Set
. . .t.ing
. . . Up
. . . DM. . . .Mult
. . . .ipat
. . .h
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1. 7. . . . . . . . . .
⁠3 .1. Setting Up DM-Multip ath
17
⁠3 .2. Ig no ring Lo c al Dis ks when G enerating Multip ath Devic es
18
⁠3 .3. Co nfig uring Sto rag e Devic es
20
⁠3 .4. Setting Up Multip athing in the initramfs File Sys tem
21
. .hapt
⁠C
. . . .er
. .4. .. T. he
. . . DM. . . .Mult
. . . .ipat
. . .h
. .Configurat
. . . . . . . . . ion
. . . .File
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2. 2. . . . . . . . . .
⁠4 .1. Co nfig uratio n File O verview
22
⁠4 .2. Co nfig uratio n File Blac klis t
23
⁠4 .2.1. Blac klis ting b y WWID
24
⁠4 .2.2. Blac klis ting By Devic e Name
24
⁠4 .2.3. Blac klis ting By Devic e Typ e
25
⁠4 .2.4. Blac klis t Exc ep tio ns
25
⁠4 .3. Co nfig uratio n File Defaults
25
⁠4 .4. Multip aths Devic e Co nfig uratio n Attrib utes
32
⁠4 .5. Co nfig uratio n File Devic es
35
. .hapt
⁠C
. . . .er
. .5.
. .DM. . . .Mult
. . . .ipat
. . . h. .Administ
. . . . . . . .rat
. . ion
. . . and
. . . .T
. .roubleshoot
. . . . . . . . . . .ing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4. 0. . . . . . . . . .
⁠5 .1. Res iz ing an O nline Multip ath Devic e
40
⁠5 .2. Mo ving ro o t File Sys tems fro m a Sing le Path Devic e to a Multip ath Devic e
40
⁠5 .3. Mo ving s wap File Sys tems fro m a Sing le Path Devic e to a Multip ath Devic e
43
⁠5 .4. The Multip ath Daemo n
44
⁠5 .5. Is s ues with Larg e Numb er o f LUNs
44
⁠5 .6 . Is s ues with q ueue_if_no _p ath feature
44
1
Red Hat Ent erprise Linux 6 DM Mult ipat h
⁠5 .7. Multip ath Co mmand O utp ut
45
⁠5 .8 . Multip ath Q ueries with multip ath Co mmand
45
⁠5 .9 . Multip ath Co mmand O p tio ns
46
⁠5 .10 . Determining Devic e Map p er Entries with the d ms etup Co mmand
⁠5 .11. Tro ub les ho o ting with the multip athd Interac tive Co ns o le
47
47
. . . . . . . . .Hist
Revision
. . . ory
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4. 9. . . . . . . . . .
⁠I.ndex
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
...........
2
Preface
Preface
This book describes the D evice Mapper Multipath (D M-Multipath) feature of Red Hat Enterprise Linux
for the Red Hat Enterprise Linux 6 release.
1. Audience
This book is intended to be used by system administrators managing systems running the Linux
operating system. It requires familiarity with Red Hat Enterprise Linux.
2. Relat ed Document at ion
For more information about using Red Hat Enterprise Linux, refer to the following resources:
Installation Guide — D ocuments relevant information regarding the installation of Red Hat
Enterprise Linux 6.
Deployment Guide — D ocuments relevant information regarding the deployment, configuration and
administration of Red Hat Enterprise Linux 6.
Storage Administration Guide — Provides instructions on how to effectively manage storage devices
and file systems on Red Hat Enterprise Linux 6.
For more information about Red Hat Cluster Suite for Red Hat Enterprise Linux 6, refer to the following
resources:
High Availability Add-On Overview — Provides a high-level overview of the Red Hat High Availability
Add-On.
Cluster Administration — Provides information about installing, configuring and managing the High
Availability Add-On.
Logical Volume Manager Administration — Provides a description of the Logical Volume Manager
(LVM), including information on running LVM in a clustered environment.
Global File System 2: Configuration and Administration — Provides information about installing,
configuring, and maintaining Red Hat GFS2 (Red Hat Global File System 2).
Load Balancer Administration — Provides information on configuring high-performance systems
and services with the Load Balancer Add-On, a set of integrated software components that
provide Linux Virtual Servers (LVS) for balancing IP load across a set of real servers.
Release Notes — Provides information about the current release of Red Hat products.
Red Hat Cluster Suite documentation and other Red Hat documents are available in HTML, PD F, and
RPM versions on the Red Hat Enterprise Linux D ocumentation CD and online at
https://access.redhat.com/site/documentation/.
3. We Need Feedback!
If you find a typographical error in this manual, or if you have thought of a way to make this manual
better, we would love to hear from you! Please submit a report in Bugzilla: http://bugzilla.redhat.com/
against the product R ed H at En t erp rise Lin u x 6 and the component d o c- D M_Mu lt ip at h . When
submitting a bug report, be sure to mention the manual's identifier:
3
Red Hat Ent erprise Linux 6 DM Mult ipat h
rh-DM_Multipath(EN)-6 (2014-10-8T15:15)
If you have a suggestion for improving the documentation, try to be as specific as possible when
describing it. If you have found an error, please include the section number and some of the
surrounding text so we can find it easily.
4 . Document Convent ions
This manual uses several conventions to highlight certain words and phrases and draw attention to
specific pieces of information.
4 .1. T ypographic Convent ions
Four typographic conventions are used to call attention to specific words and phrases. These
conventions, and the circumstances they apply to, are as follows.
Mo no -spaced Bo l d
Used to highlight system input, including shell commands, file names and paths. Also used to
highlight keys and key combinations. For example:
To see the contents of the file my_next_bestsel l i ng _no vel in your current
working directory, enter the cat my_next_bestsel l i ng _no vel command at the
shell prompt and press Enter to execute the command.
The above includes a file name, a shell command and a key, all presented in mono-spaced bold and
all distinguishable thanks to context.
Key combinations can be distinguished from an individual key by the plus sign that connects each
part of a key combination. For example:
Press Enter to execute the command.
Press C trl +Al t+F2 to switch to a virtual terminal.
The first example highlights a particular key to press. The second example highlights a key
combination: a set of three keys pressed simultaneously.
If source code is discussed, class names, methods, functions, variable names and returned values
mentioned within a paragraph will be presented as above, in mo no -spaced bo l d . For example:
File-related classes include fi l esystem for file systems, fi l e for files, and d i r for
directories. Each class has its own associated set of permissions.
Pro p o rt io n al B o ld
This denotes words or phrases encountered on a system, including application names; dialog-box
text; labeled buttons; check-box and radio-button labels; menu titles and submenu titles. For
example:
Choose Syst em → Pref eren ces → Mo u se from the main menu bar to launch
Mo u se Pref eren ces. In the Butto ns tab, select the Left-hand ed mo use check
box and click C l o se to switch the primary mouse button from the left to the right
(making the mouse suitable for use in the left hand).
To insert a special character into a g ed it file, choose Ap p licat io n s →
Accesso ries → C h aract er Map from the main menu bar. Next, choose Search →
4
Preface
Fin d … from the C h aract er Map menu bar, type the name of the character in the
Search field and click Next. The character you sought will be highlighted in the
C haracter T abl e. D ouble-click this highlighted character to place it in the T ext
to co py field and then click the C o py button. Now switch back to your document
and choose Ed it → Past e from the g ed it menu bar.
The above text includes application names; system-wide menu names and items; application-specific
menu names; and buttons and text found within a GUI interface, all presented in proportional bold
and all distinguishable by context.
Mono-spaced Bold Italic or Proportional Bold Italic
Whether mono-spaced bold or proportional bold, the addition of italics indicates replaceable or
variable text. Italics denotes text you do not input literally or displayed text that changes depending
on circumstance. For example:
To connect to a remote machine using ssh, type ssh username@ domain.name at a
shell prompt. If the remote machine is exampl e. co m and your username on that
machine is john, type ssh jo hn@ exampl e. co m.
The mo unt -o remo unt file-system command remounts the named file system.
For example, to remount the /ho me file system, the command is mo unt -o remo unt
/ho me.
To see the version of a currently installed package, use the rpm -q package
command. It will return a result as follows: package-version-release.
Note the words in bold italics above: username, domain.name, file-system, package, version and
release. Each word is a placeholder, either for text you enter when issuing a command or for text
displayed by the system.
Aside from standard usage for presenting the title of a work, italics denotes the first use of a new and
important term. For example:
Publican is a DocBook publishing system.
4 .2. Pull-quot e Convent ions
Terminal output and source code listings are set off visually from the surrounding text.
Output sent to a terminal is set in mo no -spaced ro man and presented thus:
books
books_tests
Desktop
Desktop1
documentation drafts mss
downloads
images notes
photos
scripts
stuff
svgs
svn
Source-code listings are also set in mo no -spaced ro man but add syntax highlighting as follows:
​static int kvm_vm_ioctl_deassign_device(struct kvm *kvm,
​
struct kvm_assigned_pci_dev *assigned_dev)
​
{
​
int r = 0;
​
struct kvm_assigned_dev_kernel *match;
mutex_lock(& kvm->lock);
​
match = kvm_find_assigned_dev(& kvm->arch.assigned_dev_head,
assigned_dev->assigned_dev_id);
​
​
5
Red Hat Ent erprise Linux 6 DM Mult ipat h
​
if (!match) {
printk(KERN_INFO "%s: device hasn't been assigned
​
before, "
​
"so cannot be deassigned\n", __func__);
r = -EINVAL;
goto out;
​
​
​
}
​
kvm_deassign_device(kvm, match);
​
kvm_free_assigned_device(kvm, match);
​o ut:
​
mutex_unlock(& kvm->lock);
return r;
​
​}
4 .3. Not es and Warnings
Finally, we use three visual styles to draw attention to information that might otherwise be overlooked.
Note
Notes are tips, shortcuts or alternative approaches to the task at hand. Ignoring a note should
have no negative consequences, but you might miss out on a trick that makes your life easier.
Important
Important boxes detail things that are easily missed: configuration changes that only apply to
the current session, or services that need restarting before an update will apply. Ignoring a
box labeled “ Important” will not cause data loss but may cause irritation and frustration.
Warning
Warnings should not be ignored. Ignoring warnings will most likely cause data loss.
6
⁠Chapt er 1 . Device Mapper Mult ipat hing
Chapter 1. Device Mapper Multipathing
D evice mapper multipathing (D M-Multipath) allows you to configure multiple I/O paths between
server nodes and storage arrays into a single device. These I/O paths are physical SAN connections
that can include separate cables, switches, and controllers. Multipathing aggregates the I/O paths,
creating a new device that consists of the aggregated paths.
This chapter provides a summary of the features of D M-Multipath that are new for the initial release of
Red Hat Enterprise Linux 6. Following that, this chapter provides a high-level overview of D M
Multipath and its components, as well as an overview of D M-Multipath setup.
1.1. New and Changed Feat ures
This section lists new and changed features of D M-Multipath that are included with the initial and
subsequent releases of Red Hat Enterprise Linux 6.
1.1.1. New and Changed Feat ures for Red Hat Ent erprise Linux 6.0
Red Hat Enterprise Linux 6.0 includes the following documentation and feature updates and
changes.
For the Red Hat Enterprise Linux 6 release, the initial D M-Multipath setup procedure for a basic
failover configuration has changed. You can now create the D M-Multipath configuration file and
enable D M-Multipath with the mpathco nf configuration utility, which can also load the d evi cemapper-mul ti path module, start the mul ti pathd daemon, and set chkco nfi g to start the
daemon automatically on reboot.
For information on the new setup procedure, see Section 3.1, “ Setting Up D M-Multipath” . For more
information on the mpathco nf command, see the mpathco nf(5) man page.
The Red Hat Enterprise Linux 6 release provides a new mode for setting up multipath devices,
which you set with the fi nd _mul ti paths configuration file parameter. In previous releases of
Red Hat Enterprise Linux, multipath always tried to create a multipath device for every path that
was not explicitly blacklisted. In Red Hat Enterprise Linux 6, however, if the fi nd _mul ti paths
configuration parameter is set to yes, then multipath will create a device only if one of three
conditions are met:
There are at least two non-blacklisted paths with the same WWID .
The user manually forces the device creation, by specifying a device with the mul ti path
command.
A path has the same WWID as a multipath device that was previously created (even if that
multipath device does not currently exist). For instructions on the procedure to follow if you
have previously created multipath devices when the fi nd _mul ti paths parameter was not
set, see Section 4.2, “ Configuration File Blacklist” .
This feature should allow most users to have multipath automatically choose the correct paths to
make into multipath devices, without having to edit the blacklist.
For information on the fi nd _mul ti paths configuration parameter, see Section 4.3,
“ Configuration File D efaults” .
The Red Hat Enterprise Linux 6 release provides two new path selector algorithms which
determine which path to use for the next I/O operation: q ueue-l eng th and servi ce-ti me. The
q ueue-l eng th algorithm looks at the amount of outstanding I/O to the paths to determine which
7
Red Hat Ent erprise Linux 6 DM Mult ipat h
path to use next. The servi ce-ti me algorithm looks at the amount of outstanding I/O and the
relative throughput of the paths to determine which path to use next. For more information on the
path selector parameters in the configuration file, see Chapter 4, The DM-Multipath Configuration File.
In the Red Hat Enterprise Linux 6 release, priority functions are no longer callout programs.
Instead they are dynamic shared objects like the path checker functions. The pri o _cal l o ut
parameter has been replaced by the pri o parameter. For descriptions of the supported pri o
functions, see Chapter 4, The DM-Multipath Configuration File.
In Red Hat Enterprise Linux 6, the mul ti path command output has changed format. For
information on the mul ti path command output, see Section 5.7, “ Multipath Command Output” .
In the Red Hat Enterprise Linux 6 release, the location of the multipath bi nd i ng s file is
/etc/mul ti path/bi nd i ng s.
The Red Hat Enterprise Linux 6 release provides three new d efaul ts parameters in the
mul ti path. co nf file: checker_ti meo ut, fast_i o _fai l _tmo , and d ev_l o ss_tmo . For
information on these parameters, see Chapter 4, The DM-Multipath Configuration File.
When the user_fri end l y_names option in the multipath configuration file is set to yes, the
name of a multipath device is of the form mpathn. For the Red Hat Enterprise Linux 6 release, n is
an alphabetic character, so that the name of a multipath device might be mpatha or mpathb. In
previous releases, n was an integer.
1.1.2. New and Changed Feat ures for Red Hat Ent erprise Linux 6.1
Red Hat Enterprise Linux 6.1 includes the following documentation and feature updates and
changes.
This document now contains a new chapter, Section 5.2, “ Moving root File Systems from a Single
Path D evice to a Multipath D evice” .
This document now contains a new chapter, Section 5.3, “ Moving swap File Systems from a
Single Path D evice to a Multipath D evice” .
1.1.3. New and Changed Feat ures for Red Hat Ent erprise Linux 6.2
Red Hat Enterprise Linux 6.2 includes the following documentation and feature updates and
changes.
The Red Hat Enterprise Linux 6.2 release provides a new mul ti path. co nf parameter,
rr_mi n_i o _rq , in the d efaul ts, d evi ces, and mul ti paths sections of the
mul ti path. co nf file. The rr_mi n_i o parameter no longer has an effect in Red Hat Enterprise
Linux 6.2. For information on the rr_mi n_i o _rq parameter, see Chapter 4, The DM-Multipath
Configuration File.
The d ev_l o ss_tmo configuration file parameter can now be set to infinity, which sets the actual
sysfs variable to 2147483647 seconds, or 68 years. For information on this parameter, see
Chapter 4, The DM-Multipath Configuration File.
The procedure described in Section 5.2, “ Moving root File Systems from a Single Path D evice to a
Multipath D evice” has been updated.
1.1.4 . New and Changed Feat ures for Red Hat Ent erprise Linux 6.3
Red Hat Enterprise Linux 6.3 includes the following documentation and feature updates and
changes.
8
⁠Chapt er 1 . Device Mapper Mult ipat hing
The default value of the q ueue_wi tho ut_d aemo n configuration file parameter is now set to no
by default.
The default value of the max_fd s configuration file parameter is now set to max by default.
The user_fri end l y_names configuration file parameter is now configurable in the d efaul ts,
mul ti paths, and d evi ces sections of the mul ti path. co nf configuration file.
The d efaul ts section of the mul ti path. co nf configuration file supports a new
hwtabl e_reg ex_match parameter.
For information on the configuration file parameters, see Chapter 4, The DM-Multipath Configuration File.
1.1.5. New and Changed Feat ures for Red Hat Ent erprise Linux 6.4
Red Hat Enterprise Linux 6.4 includes the following documentation and feature updates and
changes.
The d efaul ts section and the d evi ces section of the mul ti path. co nf configuration file
support a new retai n_attached _hard ware_hand l er parameter and a new d etect_pri o
parameter. For information on the configuration file parameters, see Chapter 4, The DM-Multipath
Configuration File.
This document contains a new section, Section 3.4, “ Setting Up Multipathing in the initramfs File
System” .
1.1.6. New and Changed Feat ures for Red Hat Ent erprise Linux 6.5
Red Hat Enterprise Linux 6.5 includes the following documentation and feature updates and
changes.
The d efaul ts section of the mul ti path. co nf configuration file supports a new
repl ace_wwi d e_whi tespace and a new rel o ad _rewri te parameter. The d efaul ts section
of the mul ti path. co nf file is documented in Table 4.1, “ Multipath Configuration D efaults” .
1.1.7. New and Changed Feat ures for Red Hat Ent erprise Linux 6.6
Red Hat Enterprise Linux 6.6 includes the following documentation and feature updates and
changes.
The d efaul ts section of the mul ti path. co nf configuration file supports a new fo rce_sync
parameter. The d efaul ts section of the mul ti path. co nf file is documented in Table 4.1,
“ Multipath Configuration D efaults” .
The mul ti path supports a -w and a -W, as described in Table 4.1, “ Multipath Configuration
D efaults” .
1.2. Overview of DM-Mult ipat h
D M-Multipath can be used to provide:
Redundancy
D M-Multipath can provide failover in an active/passive configuration. In an active/passive
configuration, only half the paths are used at any time for I/O. If any element of an I/O path (the
cable, switch, or controller) fails, D M-Multipath switches to an alternate path.
9
Red Hat Ent erprise Linux 6 DM Mult ipat h
Improved Performance
D M-Multipath can be configured in active/active mode, where I/O is spread over the paths in a
round-robin fashion. In some configurations, D M-Multipath can detect loading on the I/O paths
and dynamically re-balance the load.
Figure 1.1, “ Active/Passive Multipath Configuration with One RAID D evice” shows an active/passive
configuration with two I/O paths from the server to a RAID device. There are 2 HBAs on the server, 2
SAN switches, and 2 RAID controllers.
Fig u re 1.1. Act ive/Passive Mu lt ip at h C o n f ig u rat io n wit h O n e R AID D evice
In this configuration, there is one I/O path that goes through hba1, SAN1, and controller 1 and a
second I/O path that goes through hba2, SAN2, and controller2. There are many points of possible
failure in this configuration:
HBA failure
FC cable failure
SAN switch failure
Array controller port failure
With D M-Multipath configured, a failure at any of these points will cause D M-Multipath to switch to
the alternate I/O path.
Figure 1.2, “ Active/Passive Multipath Configuration with Two RAID D evices” shows a more complex
active/passive configuration with 2 HBAs on the server, 2 SAN switches, and 2 RAID devices with 2
RAID controllers each.
10
⁠Chapt er 1 . Device Mapper Mult ipat hing
Fig u re 1.2. Act ive/Passive Mu lt ip at h C o n f ig u rat io n wit h T wo R AID D evices
In the example shown in Figure 1.2, “ Active/Passive Multipath Configuration with Two RAID D evices” ,
there are two I/O paths to each RAID device (just as there are in the example shown in Figure 1.1,
“ Active/Passive Multipath Configuration with One RAID D evice” ). With D M-Multipath configured, a
failure at any of the points of the I/O path to either of the RAID devices will cause D M-Multipath to
switch to the alternate I/O path for that device.
Figure 1.3, “ Active/Active Multipath Configuration with One RAID D evice” shows an active/active
configuration with 2 HBAs on the server, 1 SAN switch, and 2 RAID controllers. There are four I/O
paths from the server to a storage device:
hba1 to controller1
hba1 to controller2
hba2 to controller1
hba2 to controller2
In this configuration, I/O can be spread among those four paths.
11
Red Hat Ent erprise Linux 6 DM Mult ipat h
Fig u re 1.3. Act ive/Act ive Mu lt ip at h C o n f ig u rat io n wit h O n e R AID D evice
1.3. St orage Array Support
By default, D M-Multipath includes support for the most common storage arrays that support D MMultipath. The supported devices can be found in the mul ti path. co nf. d efaul ts file. If your
storage array supports D M-Multipath and is not configured by default in this file, you may need to
add them to the D M-Multipath configuration file, mul ti path. co nf. For information on the D MMultipath configuration file, see Chapter 4, The DM-Multipath Configuration File.
Some storage arrays require special handling of I/O errors and path switching. These require
separate hardware handler kernel modules.
1.4 . DM-Mult ipat h Component s
Table 1.1, “ D M-Multipath Components” . describes the components of D M-Multipath.
T ab le 1.1. D M- Mu lt ip at h C o mp o n en t s
C o mp o n en t
D escrip t io n
d m_mul ti path kernel module
mpathco nf utility
mul ti path command
Reroutes I/O and supports failover for paths and path groups.
Configures and enables device mapper multipathing.
Lists and configures multipath devices. Normally started up with
/etc/rc. sysi ni t, it can also be started up by a ud ev program
whenever a block device is added.
Monitors paths; as paths fail and come back, it may initiate path
group switches. Provides for interactive changes to multipath
devices. This must be restarted for any changes to the
/etc/mul ti path. co nf file.
mul ti pathd daemon
12
⁠Chapt er 1 . Device Mapper Mult ipat hing
C o mp o n en t
D escrip t io n
kpartx command
Creates device mapper devices for the partitions on a device It is
necessary to use this command for D OS-based partitions with
D M-MP. The kpartx is provided in its own package, but the
d evi ce-mapper-mul ti path package depends on it.
1.5. DM-Mult ipat h Set up Overview
D M-Multipath includes compiled-in default settings that are suitable for common multipath
configurations. Setting up D M-multipath is often a simple procedure.
The basic procedure for configuring your system with D M-Multipath is as follows:
1. Install the d evi ce-mapper-mul ti path rpm.
2. Create the configuration file and enable multipathing with the mpathco nf command. You can
also start the multipath daemon with this command if you do not need to edit the
configuration file.
3. If necessary, edit the mul ti path. co nf configuration file to modify default values and save
the updated file.
4. Start the multipath daemon.
For detailed setup instructions for multipath configuration see Chapter 3, Setting Up DM-Multipath.
13
Red Hat Ent erprise Linux 6 DM Mult ipat h
Chapter 2. Multipath Devices
Without D M-Multipath, each path from a server node to a storage controller is treated by the system
as a separate device, even when the I/O path connects the same server node to the same storage
controller. D M-Multipath provides a way of organizing the I/O paths logically, by creating a single
multipath device on top of the underlying devices.
2.1. Mult ipat h Device Ident ifiers
Each multipath device has a World Wide Identifier (WWID ), which is guaranteed to be globally unique
and unchanging. By default, the name of a multipath device is set to its WWID . Alternately, you can
set the user_fri end l y_names option in the multipath configuration file, which sets the alias to a
node-unique name of the form mpathn.
For example, a node with two HBAs attached to a storage controller with two ports via a single
unzoned FC switch sees four devices: /d ev/sd a, /d ev/sd b, d ev/sd c, and /d ev/sd d . D MMultipath creates a single device with a unique WWID that reroutes I/O to those four underlying
devices according to the multipath configuration. When the user_fri end l y_names configuration
option is set to yes, the name of the multipath device is set to mpathn.
When new devices are brought under the control of D M-Multipath, the new devices may be seen in
two different places under the /d ev directory: /d ev/mapper/mpathn and /d ev/d m-n.
The devices in /d ev/mapper are created early in the boot process. Use these devices to access
the multipathed devices, for example when creating logical volumes.
Any devices of the form /d ev/d m-n are for internal use only and should never be used.
For information on the multipath configuration defaults, including the user_fri end l y_names
configuration option, see Section 4.3, “ Configuration File D efaults” .
You can also set the name of a multipath device to a name of your choosing by using the al i as
option in the mul ti paths section of the multipath configuration file. For information on the
mul ti paths section of the multipath configuration file, see Section 4.4, “ Multipaths D evice
Configuration Attributes” .
2.2. Consist ent Mult ipat h Device Names in a Clust er
When the user_fri end l y_names configuration option is set to yes, the name of the multipath
device is unique to a node, but it is not guaranteed to be the same on all nodes using the multipath
device. Similarly, if you set the al i as option for a device in the mul ti paths section of the
mul ti path. co nf configuration file, the name is not automatically consistent across all nodes in
the cluster. This should not cause any difficulties if you use LVM to create logical devices from the
multipath device, but if you require that your multipath device names be consistent in every node it is
recommended that you not set the user_fri end l y_names option to yes and that you not configure
aliases for the devices. By default, if you do not set user_fri end l y_names to yes or configure an
alias for a device, a device name will be the WWID for the device, which is always the same.
If you want the system-defined user-friendly names to be consistent across all nodes in the cluster,
however, you can follow this procedure:
1. Set up all of the multipath devices on one machine.
2. D isable all of your multipath devices on your other machines by running the following
commands:
14
⁠Chapt er 2 . Mult ipat h Devices
# servi ce mul ti pathd sto p
# mul ti path -F
3. Copy the /etc/mul ti path/bi nd i ng s file from the first machine to all the other machines
in the cluster.
4. Re-enable the mul ti pathd daemon on all the other machines in the cluster by running the
following command:
# servi ce mul ti pathd start
If you add a new device, you will need to repeat this process.
Similarly, if you configure an alias for a device that you would like to be consistent across the nodes
in the cluster, you should ensure that the /etc/mul ti path. co nf file is the same for each node in
the cluster by following the same procedure:
1. Configure the aliases for the multipath devices in the in the mul ti path. co nf file on one
machine.
2. D isable all of your multipath devices on your other machines by running the following
commands:
# servi ce mul ti pathd sto p
# mul ti path -F
3. Copy the /etc/mul ti path. co nf file from the first machine to all the other machines in the
cluster.
4. Re-enable the mul ti pathd daemon on all the other machines in the cluster by running the
following command:
# servi ce mul ti pathd start
When you add a new device you will need to repeat this process.
2.3. Mult ipat h Device At t ribut es
In addition to the user_fri end l y_names and al i as options, a multipath device has numerous
attributes. You can modify these attributes for a specific multipath device by creating an entry for that
device in the mul ti paths section of the multipath configuration file. For information on the
mul ti paths section of the multipath configuration file, see Section 4.4, “ Multipaths D evice
Configuration Attributes” .
2.4 . Mult ipat h Devices in Logical Volumes
After creating multipath devices, you can use the multipath device names just as you would use a
physical device name when creating an LVM physical volume. For example, if
/d ev/mapper/mpatha is the name of a multipath device, the following command will mark
/d ev/mapper/mpatha as a physical volume.
pvcreate /dev/mapper/mpatha
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Red Hat Ent erprise Linux 6 DM Mult ipat h
You can use the resulting LVM physical device when you create an LVM volume group just as you
would use any other LVM physical device.
Note
If you attempt to create an LVM physical volume on a whole device on which you have
configured partitions, the pvcreate command will fail. Note that the Anaconda and Kickstart
installation programs create empty partition tables if you do not specify otherwise for every
block device. If you wish to use the whole device rather than a partition, you must remove the
existing partitions from the device. You can remove existing partitions with the kpartx -d and
the fd i sk commands. If your system has block devices that are greater that 2Tb, you can use
the parted command to remove partitions.
When you create an LVM logical volume that uses active/passive multipath arrays as the underlying
physical devices, you should include filters in the l vm. co nf to exclude the disks that underlie the
multipath devices. This is because if the array automatically changes the active path to the passive
path when it receives I/O, multipath will failover and failback whenever LVM scans the passive path if
these devices are not filtered. For active/passive arrays that require a command to make the passive
path active, LVM prints a warning message when this occurs.
To filter all SCSI devices in the LVM configuration file (l vm. co nf), include the following filter in the
d evi ces section of the file.
filter = [ "r/block/", "r/disk/", "r/sd.*/", "a/.*/" ]
16
⁠Chapt er 3. Set t ing Up DM- Mult ipat h
Chapter 3. Setting Up DM-Multipath
This chapter provides step-by-step example procedures for configuring D M-Multipath. It includes the
following procedures:
Basic D M-Multipath setup
Ignoring local disks
Adding more devices to the configuration file
Starting multipath in the i ni tramfs file system
3.1. Set t ing Up DM-Mult ipat h
Before setting up D M-Multipath on your system, ensure that your system has been updated and
includes the d evi ce-mapper-mul ti path package.
You set up multipath with the mpathco nf utility, which creates the multipath configuration file
/etc/mul ti path. co nf.
If the /etc/mul ti path. co nf file already exists, the mpathco nf utility will edit it.
If the /etc/mul ti path. co nf file does not exist, the mpathco nf utility will use the
/usr/share/d o c/d evi ce-mapper-mul ti path-0 . 4 . 9 /mul ti path. co nf file as the
starting file.
If the /usr/share/d o c/d evi ce-mapper-mul ti path-0 . 4 . 9 /mul ti path. co nf file does
not exist the mpathco nf utility will create the /etc/mul ti path. co nf file from scratch.
If you do not need to edit the /etc/mul ti path. co nf file, you can set up D M-Multipath for a basic
failover configuration by running the following command. This command enables the multipath
configuration file and starts the mul ti pathd daemon.
# mpathco nf --enabl e --wi th_mul ti pathd y
If you need to edit the /etc/mul ti path. co nf file before starting the mul ti pathd daemon. use the
following procedure to set up D M-Multipath for a basic failover configuration.
1. Run the mpathco nf command with the --enabl e option specified:
# mpathco nf --enabl e
For information on additional options to the mpathco nf command you may require, see the
mpathco nf man page or run the mpathco nf command with the --hel p option specified.
# mpathco nf --hel p
usage: /sbin/mpathconf <command>
Commands:
Enable: --enable
Disable: --disable
Set user_friendly_names (Default n): --user_friendly_names <y|n>
Set find_multipaths (Default n): --find_multipaths <y|n>
17
Red Hat Ent erprise Linux 6 DM Mult ipat h
Load the dm-multipath modules on enable (Default y): --with_module
<y|n>
start/stop/reload multipathd (Default n): --with_multipathd <y|n>
chkconfig on/off multipathd (Default y): --with_chkconfig <y|n>
2. Edit the /etc/mul ti path. co nf file if necessary. The default settings for D M-Multipath are
compiled in to the system and do not need to be explicitly set in the /etc/mul ti path. co nf
file.
The default value of path_g ro upi ng _po l i cy is set to fai l o ver, so in this example you
do not need to edit the /etc/mul ti path. co nf file. For information on changing the values
in the configuration file to something other than the defaults, see Chapter 4, The DM-Multipath
Configuration File.
The initial defaults section of the configuration file configures your system so that the names
of the multipath devices are of the form mpathn; without this setting, the names of the
multipath devices would be aliased to the WWID of the device.
3. Save the configuration file and exit the editor, if necessary.
4. Execute the following command:
# servi ce mul ti pathd start
Since the value of user_fri end l y_name is set to yes in the configuration file, the multipath
devices will be created as /d ev/mapper/mpathn. For information on setting the name of the device
to an alias of your choosing, see Chapter 4, The DM-Multipath Configuration File.
If you do not want to use user friendly names, you can run the following command:
# mpathco nf --enabl e --user_fri end l y_names n
Note
If you find that you need to edit the multipath configuration file after you have started the
multipath daemon, you must execute the servi ce mul ti pathd rel o ad command for the
changes to take effect.
3.2. Ignoring Local Disks when Generat ing Mult ipat h Devices
Some machines have local SCSI cards for their internal disks. D M-Multipath is not recommended for
these devices. If you set the fi nd _mul ti paths configuration parameter to yes, you should not
have to blacklist these devices. For information on the fi nd _mul ti paths configuration parameter,
see Section 4.3, “ Configuration File D efaults” .
If you do not set the fi nd _mul ti paths configuration parameter to yes, can use the following
procedure to modify the multipath configuration file to ignore the local disks when configuring
multipath.
1. D etermine which disks are the internal disks and mark them as the ones to blacklist.
18
⁠Chapt er 3. Set t ing Up DM- Mult ipat h
In this example, /d ev/sd a is the internal disk. Note that as originally configured in the
default multipath configuration file, executing the mul ti path -v2 shows the local disk,
/d ev/sd a, in the multipath map.
For further information on the mul ti path command output, see Section 5.7, “ Multipath
Command Output” .
# mul ti path -v2
create: SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1 undef
WINSYS,SF2372
size=33 GB features="0" hwhandler="0" wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 0:0:0:0 sda 8:0 [--------device-mapper ioctl cmd 9 failed: Invalid argument
device-mapper ioctl cmd 14 failed: No such device or address
create: 3600a0b80001327d80000006d43621677 undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:0 sdb 8:16 undef ready running
`- 3:0:0:0 sdf 8:80 undef ready running
create: 3600a0b80001327510000009a436215ec undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:1 sdc 8:32 undef ready running
`- 3:0:0:1 sdg 8:96 undef ready running
create: 3600a0b80001327d800000070436216b3 undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:2 sdd 8:48 undef ready running
`- 3:0:0:2 sdg 8:112 undef ready running
create: 3600a0b80001327510000009b4362163e undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:3 sdd 8:64 undef ready running
`- 3:0:0:3 sdg 8:128 undef ready running
2. In order to prevent the device mapper from mapping /d ev/sd a in its multipath maps, edit the
blacklist section of the /etc/mul ti path. co nf file to include this device. Although you
could blacklist the sd a device using a d evno d e type, that would not be safe procedure since
/d ev/sd a is not guaranteed to be the same on reboot. To blacklist individual devices, you
can blacklist using the WWID of that device.
Note that in the output to the mul ti path -v2 command, the WWID of the /d ev/sd a device
is SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1. To blacklist this device, include
the following in the /etc/mul ti path. co nf file.
blacklist {
wwid SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1
}
19
Red Hat Ent erprise Linux 6 DM Mult ipat h
3. After you have updated the /etc/mul ti path. co nf file, you must manually tell the
mul ti pathd daemon to reload the file. The following command reloads the updated
/etc/mul ti path. co nf file.
# servi ce mul ti pathd rel o ad
4. Run the following command to remove the multipath device:
# mul ti path -f SIBM-ESXSST 336 732LC ____F3ET 0 EP 0 Q 0 0 0 0 724 28BX1
5. To check whether the device removal worked, you can run the mul ti path -l l command to
display the current multipath configuration. For information on the mul ti path -l l
command, see Section 5.8, “ Multipath Queries with multipath Command” .
To check that the blacklisted device was not added back, you can run the mul ti path
command, as in the following example. The mul ti path command defaults to a verbosity
level of v2 if you do not specify specify a -v option.
# mul ti path
create: 3600a0b80001327d80000006d43621677 undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:0 sdb 8:16 undef ready running
`- 3:0:0:0 sdf 8:80 undef ready running
create: 3600a0b80001327510000009a436215ec undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:1 sdc 8:32 undef ready running
`- 3:0:0:1 sdg 8:96 undef ready running
create: 3600a0b80001327d800000070436216b3 undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:2 sdd 8:48 undef ready running
`- 3:0:0:2 sdg 8:112 undef ready running
create: 3600a0b80001327510000009b4362163e undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:3 sdd 8:64 undef ready running
`- 3:0:0:3 sdg 8:128 undef ready running
3.3. Configuring St orage Devices
By default, D M-Multipath includes support for the most common storage arrays that support D MMultipath. The default configuration values, including supported devices, can be found in the
mul ti path. co nf. d efaul ts file.
If you need to add a storage device that is not supported by default as a known multipath device, edit
the /etc/mul ti path. co nf file and insert the appropriate device information.
20
⁠Chapt er 3. Set t ing Up DM- Mult ipat h
For example, to add information about the HP Open-V series the entry looks like this, where % n is the
device name:
devices {
device {
vendor "HP"
product "OPEN-V."
getuid_callout "/lib/udev/scsi_id --whitelisted -device=/dev/%n"
}
}
For more information on the d evi ces section of the configuration file, see Section 4.5,
“ Configuration File D evices” .
3.4 . Set t ing Up Mult ipat hing in t he init ramfs File Syst em
You can set up multipathing in the i ni tramfs file system. After configuring multipath, you can
rebuild the i ni tramfs file system with the multipath configuration files by executing the d racut
command with the following options:
# d racut --fo rce --ad d mul ti path --i ncl ud e /etc/mul ti path /etc/mul ti path
If you run multipath from the i ni tramfs file system and you make any changes to the multipath
configuration files, you must rebuild the i ni tramfs file system for the changes to take effect.
21
Red Hat Ent erprise Linux 6 DM Mult ipat h
Chapter 4. The DM-Multipath Configuration File
By default, D M-Multipath provides configuration values for the most common uses of multipathing. In
addition, D M-Multipath includes support for the most common storage arrays that support D MMultipath. The default configuration values and the supported devices can be found in the
/usr/share/d o c/d evi ce-mapper-mul ti path-0 . 4 . 9 /mul ti path. co nf. d efaul ts file.
You can override the default configuration values for D M-Multipath by editing the
/etc/mul ti path. co nf configuration file. If necessary, you can also add a storage array that is
not supported by default to the configuration file.
Note
You can run set up multipathing in the i ni tramfs file system. If you run multipath from the
i ni tramfs file system and you make any changes to the multipath configuration files, you
must rebuild the i ni tramfs file system for the changes to take effect. For information on
rebuilding the i ni tramfs file system with multipath, refer to Section 3.4, “ Setting Up
Multipathing in the initramfs File System” .
This chapter provides information on parsing and modifying the mul ti path. co nf file. It contains
sections on the following topics:
Configuration file overview
Configuration file blacklist
Configuration file defaults
Configuration file multipaths
Configuration file devices
In the multipath configuration file, you need to specify only the sections that you need for your
configuration, or that you wish to change from the default values specified in the
mul ti path. co nf. d efaul ts file. If there are sections of the file that are not relevant to your
environment or for which you do not need to override the default values, you can leave them
commented out, as they are in the initial file.
The configuration file allows regular expression description syntax.
An annotated version of the configuration file can be found in /usr/share/d o c/d evi ce-mappermul ti path-0 . 4 . 9 /mul ti path. co nf. anno tated .
4 .1. Configurat ion File Overview
The multipath configuration file is divided into the following sections:
b lacklist
Listing of specific devices that will not be considered for multipath.
b lacklist _excep t io n s
Listing of multipath candidates that would otherwise be blacklisted according to the
parameters of the blacklist section.
22
⁠Chapt er 4 . T he DM- Mult ipat h Configurat ion File
d ef au lt s
General default settings for D M-Multipath.
mu lt ip at h s
Settings for the characteristics of individual multipath devices. These values overwrite what
is specified in the d efaul ts and d evi ces sections of the configuration file.
d evices
Settings for the individual storage controllers. These values overwrite what is specified in
the d efaul ts section of the configuration file. If you are using a storage array that is not
supported by default, you may need to create a d evi ces subsection for your array.
When the system determines the attributes of a multipath device, first it checks the multipath settings,
then the per devices settings, then the multipath system defaults.
4 .2. Configurat ion File Blacklist
The bl ackl i st section of the multipath configuration file specifies the devices that will not be used
when the system configures multipath devices. D evices that are blacklisted will not be grouped into a
multipath device.
In older releases of Red Hat Enterprise Linux, multipath always tried to create a multipath device for
every path that was not explicitly blacklisted. In Red Hat Enterprise Linux 6, however, if the
fi nd _mul ti paths configuration parameter is set to yes, then multipath will create a device only if
one of three conditions are met:
There are at least two non-blacklisted paths with the same WWID .
The user manually forces the creation of the device by specifying a device with the mul ti path
command.
A path has the same WWID as a multipath device that was previously created (even if that
multipath device does not currently exist). Whenever a multipath device is created, multipath
remembers the WWID of the device so that it will automatically create the device again as soon as
it sees a path with that WWID . This allows you to have multipath automatically choose the correct
paths to make into multipath devices, without have to edit the multipath blacklist.
If you have previously created a multipath device without using the fi nd _mul ti paths
parameter and then you later set the parameter to yes, you may need to remove the WWID s of any
device you do not want created as a multipath device from the /etc/mul ti path/wwi d s file. The
following shows a sample /etc/mul ti path/wwi d s file. The WWID s are enclosed by slashes (/):
# Multipath wwids, Version : 1.0
# NOTE: This file is automatically maintained by multipath and
multipathd.
# You should not need to edit this file in normal circumstances.
#
# Valid WWIDs:
/3600d0230000000000e13955cc3757802/
/3600d0230000000000e13955cc3757801/
/3600d0230000000000e13955cc3757800/
/3600d02300069c9ce09d41c31f29d4c00/
/SWINSYS SF2372
0E13955CC3757802/
/3600d0230000000000e13955cc3757803/
23
Red Hat Ent erprise Linux 6 DM Mult ipat h
With the fi nd _mul ti paths parameter set to yes, you need to blacklist only the devices with
multiple paths that you do not want to be multipathed. Because of this, it will generally not be
necessary to blacklist devices.
If you do need to blacklist devices, you can do so according to the following criteria:
By WWID , as described in Section 4.2.1, “ Blacklisting by WWID ”
By device name, as described in Section 4.2.2, “ Blacklisting By D evice Name”
By device type, as described in Section 4.2.3, “ Blacklisting By D evice Type”
By default, a variety of device types are blacklisted, even after you comment out the initial blacklist
section of the configuration file. For information, see Section 4.2.2, “ Blacklisting By D evice Name” .
4 .2.1. Blacklist ing by WWID
You can specify individual devices to blacklist by their World-Wide ID entification with a wwi d entry in
the bl ackl i st section of the configuration file.
The following example shows the lines in the configuration file that would blacklist a device with a
WWID of 26353900f02796769.
blacklist {
wwid 26353900f02796769
}
4 .2.2. Blacklist ing By Device Name
You can blacklist device types by device name so that they will not be grouped into a multipath
device by specifying a d evno d e entry in the bl ackl i st section of the configuration file.
The following example shows the lines in the configuration file that would blacklist all SCSI devices,
since it blacklists all sd* devices.
blacklist {
devnode "^sd[a-z]"
}
You can use a d evno d e entry in the bl ackl i st section of the configuration file to specify
individual devices to blacklist rather than all devices of a specific type. This is not recommended,
however, since unless it is statically mapped by ud ev rules, there is no guarantee that a specific
device will have the same name on reboot. For example, a device name could change from
/d ev/sd a to /d ev/sd b on reboot.
By default, the following d evno d e entries are compiled in the default blacklist; the devices that these
entries blacklist do not generally support D M-Multipath. To enable multipathing on any of these
devices, you would need to specify them in the bl ackl i st_excepti o ns section of the
configuration file, as described in Section 4.2.4, “ Blacklist Exceptions” .
blacklist {
devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
devnode "^(td|hd)[a-z]"
}
4 .2.3. Blacklist ing By Device T ype
24
⁠Chapt er 4 . T he DM- Mult ipat h Configurat ion File
4 .2.3. Blacklist ing By Device T ype
You can specify specific device types in the bl ackl i st section of the configuration file with a
d evi ce section. The following example blacklists all IBM D S4200 and HP devices.
blacklist {
device {
vendor "IBM"
product "3S42"
#DS4200 Product 10
}
device {
vendor "HP"
product "*"
}
}
4 .2.4 . Blacklist Except ions
You can use the bl ackl i st_excepti o ns section of the configuration file to enable multipathing
on devices that have been blacklisted by default.
For example, if you have a large number of devices and want to multipath only one of them (with the
WWID of 3600d0230000000000e13955cc3757803), instead of individually blacklisting each of the
devices except the one you want, you could instead blacklist all of them, and then allow only the one
you want by adding the following lines to the /etc/mul ti path. co nf file.
blacklist {
wwid "*"
}
blacklist_exceptions {
wwid "3600d0230000000000e13955cc3757803"
}
When specifying devices in the bl ackl i st_excepti o ns section of the configuration file, you must
specify the exceptions in the same way they were specified in the blacklist. For example, a WWID
exception will not apply to devices specified by a d evno d e blacklist entry, even if the blacklisted
device is associated with that WWID . Similarly, d evno d e exceptions apply only to d evno d e entries,
and d evi ce exceptions apply only to device entries.
4 .3. Configurat ion File Default s
The /etc/mul ti path. co nf configuration file includes a d efaul ts section that sets the
user_fri end l y_names parameter to yes, as follows.
defaults {
user_friendly_names yes
}
This overwrites the default value of the user_fri end l y_names parameter.
The configuration file includes a template of configuration defaults. This section is commented out,
as follows.
25
Red Hat Ent erprise Linux 6 DM Mult ipat h
#defaults {
#
udev_dir
#
polling_interval
#
path_selector
#
path_grouping_policy
#
getuid_callout
device=/dev/%n"
# prio
const
# path_checker directio
# rr_min_io 1000
# rr_weight uniform
# failback manual
# no_path_retry fail
# user_friendly_names no
#}
/dev
5
"round-robin 0"
failover
"/lib/udev/scsi_id --whitelisted --
To overwrite the default value for any of the configuration parameters, you can copy the relevant line
from this template into the d efaul ts section and uncomment it. For example, to overwrite the
path_g ro upi ng _po l i cy parameter so that it is mul ti bus rather than the default value of
fai l o ver, copy the appropriate line from the template to the initial d efaul ts section of the
configuration file, and uncomment it, as follows.
defaults {
user_friendly_names
path_grouping_policy
}
yes
multibus
Table 4.1, “ Multipath Configuration D efaults” describes the attributes that are set in the d efaul ts
section of the mul ti path. co nf configuration file. These values are used by D M-Multipath unless
they are overwritten by the attributes specified in the d evi ces and mul ti paths sections of the
mul ti path. co nf file.
Note
As of the Red Hat Enterprise Linux 6.0 release, the mo d e, ui d , and g i d parameters have
been deprecated. Permissions for device-mapper devices (including mulitpath mappings) are
set by means of ud ev rules. There is a template file in /usr/share/d o c/d evi cemapper-version called 12-d m-permi ssi o ns. rul es which you can use and place in the
/etc/ud ev/rul es. d directory for it to take effect.
T ab le 4 .1. Mu lt ip at h C o n f ig u rat io n D ef au lt s
At t rib u t e
po l l i ng _i nterval
ud ev_d i r
mul ti path_d i r
26
D escrip t io n
Specifies the interval between two path checks in seconds. For
properly functioning paths, the interval between checks will
gradually increase to (4 * po l l i ng _i nterval ). The default
value is 5.
The directory where ud ev device nodes are created. The default
value is /d ev.
The directory where the dynamic shared objects are stored. The
default value is system dependent, commonly /l i b/mul ti path.
⁠Chapt er 4 . T he DM- Mult ipat h Configurat ion File
At t rib u t e
fi nd _mul ti paths
D escrip t io n
D efines the mode for setting up multipath devices. If this
parameter is set to yes, then multipath will not try to create a
device for every non-blacklisted path. Instead multipath will
create a device only if one of three conditions are met:
- There are at least two non-blacklisted paths with the same
WWID .
- The user manually forces the creation of the device by
specifying a device with the mul ti path command.
- A path has the same WWID as a multipath device that was
previously created. Whenever a multipath device is created with
fi nd _mul ti paths set, multipath remembers the WWID of the
device so that it will automatically create the device again as
soon as it sees a path with that WWID . This allows you to have
multipath automatically choose the correct paths to make into
multipath devices, without having to edit the multipath blacklist.
For instructions on the procedure to follow if you have previously
created multipath devices when the fi nd _mul ti paths
parameter was not set, see Section 4.2, “ Configuration File
Blacklist” .
The default value is no .
verbo si ty
The default verbosity. Higher values increase the verbosity level.
Valid levels are between 0 and 6. The default value is 2.
path_sel ecto r
Specifies the default algorithm to use in determining what path to
use for the next I/O operation. Possible values include:
ro und -ro bi n 0 : Loop through every path in the path group,
sending the same amount of I/O to each.
q ueue-l eng th 0 : Send the next bunch of I/O down the path
with the least number of outstanding I/O requests.
servi ce-ti me 0 : Send the next bunch of I/O down the path
with the shortest estimated service time, which is determined by
dividing the total size of the outstanding I/O to each path by its
relative throughput.
The default value is ro und -ro bi n 0 .
27
Red Hat Ent erprise Linux 6 DM Mult ipat h
At t rib u t e
path_g ro upi ng _po l i cy
D escrip t io n
Specifies the default path grouping policy to apply to unspecified
multipaths. Possible values include:
fai l o ver: 1 path per priority group.
mul ti bus: all valid paths in 1 priority group.
g ro up_by_seri al : 1 priority group per detected serial number.
g ro up_by_pri o : 1 priority group per path priority value.
Priorities are determined by callout programs specified as global,
per-controller, or per-multipath options.
g ro up_by_no d e_name: 1 priority group per target node name.
Target node names are fetched in
/sys/cl ass/fc_transpo rt/targ et*/no d e_name.
The default value is fai l o ver.
g etui d _cal l o ut
Specifies the default program and arguments to call out to obtain
a unique path identifier. An absolute path is required.
The default value is /l i b/ud ev/scsi _i d --whi tel i sted -d evi ce= /d ev/%n.
pri o
Specifies the default function to call to obtain a path priority
value. For example, the ALUA bits in SPC-3 provide an
exploitable pri o value. Possible values include:
co nst: Set a priority of 1 to all paths.
emc: Generate the path priority for EMC arrays.
al ua: Generate the path priority based on the SCSI-3 ALUA
settings.
tpg _pref: Generate the path priority based on the SCSI-3 ALUA
settings, using the preferred port bit.
o ntap: Generate the path priority for NetApp arrays.
rd ac: Generate the path priority for LSI/Engenio RD AC controller.
hp_sw: Generate the path priority for Compaq/HP controller in
active/standby mode.
hd s: Generate the path priority for Hitachi HD S Modular storage
arrays.
The default value is co nst.
28
⁠Chapt er 4 . T he DM- Mult ipat h Configurat ion File
At t rib u t e
features
D escrip t io n
The default extra features of multipath devices, using the format:
" number_of_features_plus_arguments feature1 ..." .
Possible values for features include:
q ueue_i f_no _path, which is the same as setting
no _path_retry to q ueue. For information on issues that may
arise when using this feature, see Section 5.6, “ Issues with
queue_if_no_path feature” .
retai n_attached _hw_hand l er: (Red Hat Enterprise Linux
Release 6.4 and later) If this parameter is set to yes and the scsi
layer has already attached a hardware handler to the path
device, multipath will not force the device to use the
hard ware_hand l er specified by the mul ti path. co nf file. If
the scsi layer has not attached a hardware handler, multipath will
continue to use its configured hardware handler as usual. The
default value is no .
pg _i ni t_retri es n: Retry path group initialization up to n
times before failing where 1 <= n <= 50.
pg _i ni t_d el ay_msecs n: Wait n milliseconds between path
group initialization retries where 0 <= n <= 60000.
path_checker
Specifies the default method used to determine the state of the
paths. Possible values include:
read secto r0 : Read the first sector of the device.
tur: Issue a T EST UNIT R EAD Y to the device.
emc_cl ari i o n: Query the EMC Clariion specific EVPD page
0xC0 to determine the path.
hp_sw: Check the path state for HP storage arrays with
Active/Standby firmware.
rd ac: Check the path stat for LSI/Engenio RD AC storage
controller.
d i recti o : Read the first sector with direct I/O.
The default value is d i recti o .
29
Red Hat Ent erprise Linux 6 DM Mult ipat h
At t rib u t e
fai l back
D escrip t io n
Manages path group failback.
A value of i mmed i ate specifies immediate failback to the highest
priority path group that contains active paths.
A value of manual specifies that there should not be immediate
failback but that failback can happen only with operator
intervention.
A value of fo l l o wo ver specifies that automatic failback should
be performed when the first path of a path group becomes active.
This keeps a node from automatically failing back when another
node requested the failover.
A numeric value greater than zero specifies deferred failback,
expressed in seconds.
The default value is manual .
rr_mi n_i o
rr_mi n_i o _rq
rr_wei g ht
no _path_retry
Specifies the number of I/O requests to route to a path before
switching to the next path in the current path group. This setting
is only for systems running kernels older than 2.6.31. Newer
systems should use rr_mi n_i o _rq . The default value is 1000.
Specifies the number of I/O requests to route to a path before
switching to the next path in the current path group, using
request-based device-mapper-multipath. This setting should be
used on systems running current kernels. On systems running
kernels older than 2.6.31, use rr_mi n_i o . The default value is 1.
If set to pri o ri ti es, then instead of sending rr_mi n_i o
requests to a path before calling path_sel ecto r to choose the
next path, the number of requests to send is determined by
rr_mi n_i o times the path's priority, as determined by the pri o
function. If set to uni fo rm, all path weights are equal. The
default value is uni fo rm.
A numeric value for this attribute specifies the number of times the
system should attempt to use a failed path before disabling
queueing.
A value of fai l indicates immediate failure, without queueing.
A value of q ueue indicates that queueing should not stop until
the path is fixed.
The default value is 0.
user_fri end l y_names
q ueue_wi tho ut_d aemo n
30
If set to yes, specifies that the system should use the
/etc/mul ti path/bi nd i ng s file to assign a persistent and
unique alias to the multipath, in the form of mpathn. If set to no ,
specifies that the system should use the WWID as the alias for the
multipath. In either case, what is specified here will be overridden
by any device-specific aliases you specify in the mul ti paths
section of the configuration file. The default value is no .
If set to no , the mul ti pathd daemon will disable queueing for all
devices when it is shut down. The default value is no .
⁠Chapt er 4 . T he DM- Mult ipat h Configurat ion File
At t rib u t e
fl ush_o n_l ast_d el
max_fd s
checker_ti meo ut
fast_i o _fai l _tmo
d ev_l o ss_tmo
hwtabl e_reg ex_match
D escrip t io n
If set to yes, the mul ti pathd daemon will disable queueing
when the last path to a device has been deleted. The default
value is no .
Sets the maximum number of open file descriptors that can be
opened by multipath and the mul ti pathd daemon. This is
equivalent to the ul i mi t -n command. As of the Red Hat
Enterprise Linux 6.3 release, the default value is max, which sets
this to the system limit from /pro c/sys/fs/nr_o pen. For earlier
releases, if this is not set the maximum number of open file
descriptors is taken from the calling process; it is usually 1024.
To be safe, this should be set to the maximum number of paths
plus 32, if that number is greater than 1024.
The timeout to use for prioritizers and path checkers that issue
SCSI commands with an explicit timeout, in seconds. The default
value is taken from sys/bl o ck/sd x/d evi ce/ti meo ut.
The number of seconds the SCSI layer will wait after a problem
has been detected on an FC remote port before failing I/O to
devices on that remote port. This value should be smaller than
the value of d ev_l o ss_tmo . Setting this to o ff will disable the
timeout. The default value is determined by the OS.
The number of seconds the SCSI layer will wait after a problem
has been detected on an FC remote port before removing it from
the system. Setting this to infinity will set this to 2147483647
seconds, or 68 years. The default value is determined by the OS.
(Red Hat Enterprise Linux Release 6.3 and later) Controls how
multipath integrates the device configurations from the d evi ces
section of the configuration file with the built-in device
configurations.
Each device configuration in the d evi ces section of the
mul ti path. co nf file will either create its own device
configuration or it will modify one of the built-in device
configurations. Prior to Red Hat Enterprise Linux 6.3, if the
vendor, product, and revision strings in a user's device
configuration exactly matched those strings in a built-in device
configuration, the built-in configuration was modified by the
options in the user's configuration. Otherwise. the user's device
configuration was treated as a new configuration.
If hwtabl e_reg ex_match is set to yes, a regular expression
match is used instead. The vendor, product, and revision strings
are all regular expressions. The user device configuration values
for these options are matched against the built-in device
configuration values. This match works the same way that an
actual device's vendor product and revision strings are matched
against a device configuration's strings to see which
configuration should be used for the device. If the user's device
configuration matches, then the built-in configuration is modified
by the options in the user's configuration. Otherwise the user's
device configuration is treated as a new configuration.
31
Red Hat Ent erprise Linux 6 DM Mult ipat h
At t rib u t e
D escrip t io n
retai n_attached _hw_han
d l er
(Red Hat Enterprise Linux Release 6.4 and later) If this parameter
is set to yes and the scsi layer has already attached a hardware
handler to the path device, multipath will not force the device to
use the hard ware_hand l er specified by the mul ti path. co nf
file. If the scsi layer has not attached a hardware handler,
multipath will continue to use its configured hardware handler as
usual. The default value is no .
(Red Hat Enterprise Linux Release 6.4 and later) If this is set to
yes, multipath will first check if the device supports ALUA, and if
so it will automatically assign the device the al ua prioritizer. If
the device doesn't support ALUA, it will determine the prioritizer as
it always does. The default value is no .
(Red Hat Enterprise Linux Release 6.5 and later) If this is set to
yes, the default g etui d _cal l o ut for all devices that use this
parameter will be changed to include --repl ace-whi tespace.
(Red Hat Enterprise Linux Release 6.5 and later) If this is set to
yes, the mul ti pathd daemon will listen to path device change
events and if a device has become read/write it will reload the
multipath device.
(Red Hat Enterprise Linux Release 6.6 and later) If this is set to
" yes" , it prevents path checkers from running in async mode.
d etect_pri o
repl ace_wwi d _whi tespac
e
rel o ad _read wri te
fo rce_sync
4 .4 . Mult ipat hs Device Configurat ion At t ribut es
Table 4.2, “ Multipath Attributes” shows the attributes that you can set in the mul ti paths section of
the mul ti path. co nf configuration file for each specific multipath device. These attributes apply
only to the one specified multipath. These defaults are used by D M-Multipath and override attributes
set in the d efaul ts and d evi ces sections of the mul ti path. co nf file.
T ab le 4 .2. Mu lt ip at h At t rib u t es
At t rib u t e
wwi d
al i as
path_g ro upi ng _po l i cy
D escrip t io n
Specifies the WWID of the multipath device to which the
mul ti path attributes apply. This parameter is mandatory for this
section of the mul ti path. co nf file.
Specifies the symbolic name for the multipath device to which the
mul ti path attributes apply. If you are using
user_fri end l y_names, do not set this value to mpathn; this
may conflict with an automatically assigned user friendly name
and give you incorrect device node names.
Specifies the default path grouping policy to apply to unspecified
multipaths. Possible values include:
fai l o ver = 1 path per priority group
mul ti bus = all valid paths in 1 priority group
g ro up_by_seri al = 1 priority group per detected serial number
g ro up_by_pri o = 1 priority group per path priority value
g ro up_by_no d e_name = 1 priority group per target node name
32
⁠Chapt er 4 . T he DM- Mult ipat h Configurat ion File
At t rib u t e
path_sel ecto r
D escrip t io n
Specifies the default algorithm to use in determining what path to
use for the next I/O operation. Possible values include:
ro und -ro bi n 0 : Loop through every path in the path group,
sending the same amount of I/O to each.
q ueue-l eng th 0 : Send the next bunch of I/O down the path
with the least number of outstanding I/O requests.
servi ce-ti me 0 : Send the next bunch of I/O down the path
with the shortest estimated service time, which is determined by
dividing the total size of the outstanding I/O to each path by its
relative throughput.
fai l back
Manages path group failback.
A value of i mmed i ate specifies immediate failback to the highest
priority path group that contains active paths.
A value of manual specifies that there should not be immediate
failback but that failback can happen only with operator
intervention.
A value of fo l l o wo ver specifies that automatic failback should
be performed when the first path of a path group becomes active.
This keeps a node from automatically failing back when another
node requested the failover.
A numeric value greater than zero specifies deferred failback,
expressed in seconds.
pri o
Specifies the default function to call to obtain a path priority
value. For example, the ALUA bits in SPC-3 provide an
exploitable pri o value. Possible values include:
co nst: Set a priority of 1 to all paths.
emc: Generate the path priority for EMC arrays.
al ua: Generate the path priority based on the SCSI-3 ALUA
settings.
tpg _pref: Generate the path priority based on the SCSI-3 ALUA
settings, using the preferred port bit.
o ntap: Generate the path priority for NetApp arrays.
rd ac: Generate the path priority for LSI/Engenio RD AC controller.
hp_sw: Generate the path priority for Compaq/HP controller in
active/standby mode.
hd s: Generate the path priority for Hitachi HD S Modular storage
arrays.
33
Red Hat Ent erprise Linux 6 DM Mult ipat h
At t rib u t e
no _path_retry
D escrip t io n
A numeric value for this attribute specifies the number of times the
system should attempt to use a failed path before disabling
queueing.
A value of fai l indicates immediate failure, without queueing.
A value of q ueue indicates that queueing should not stop until
the path is fixed.
rr_mi n_i o
rr_mi n_i o _rq
rr_wei g ht
fl ush_o n_l ast_d el
user_fri end l y_names
Specifies the number of I/O requests to route to a path before
switching to the next path in the current path group. This setting
is only for systems running kernels older that 2.6.31. Newer
systems should use rr_mi n_i o _rq . The default value is 1000.
Specifies the number of I/O requests to route to a path before
switching to the next path in the current path group, using
request-based device-mapper-multipath. This setting should be
used on systems running current kernels. On systems running
kernels older than 2.6.31, use rr_mi n_i o . The default value is 1.
If set to pri o ri ti es, then instead of sending rr_mi n_i o
requests to a path before calling path_sel ecto r to choose the
next path, the number of requests to send is determined by
rr_mi n_i o times the path's priority, as determined by the pri o
function. If set to uni fo rm, all path weights are equal.
If set to yes, then multipath will disable queueing when the last
path to a device has been deleted.
If set to yes, specifies that the system should use the
/etc/mul ti path/bi nd i ng s file to assign a persistent and
unique alias to the multipath, in the form of mpathn. If set to no ,
specifies that the system should use use the WWID as the alias
for the multipath. In either case, what is specified here will be
overridden by any device-specific aliases you specify in the
mul ti paths section of the configuration file.
The following example shows multipath attributes specified in the configuration file for two specific
multipath devices. The first device has a WWID of 36 0 0 50 8b4 0 0 0 156 d 70 0 0 120 0 0 0 0 b0 0 0 0 and
a symbolic name of yel l o w.
The second multipath device in the example has a WWID of 1D EC _____321816 7584 74 and a
symbolic name of red . In this example, the rr_wei g ht attributes is set to pri o ri ti es.
multipaths {
multipath {
wwid
alias
path_grouping_policy
path_selector
failback
rr_weight
no_path_retry
}
multipath {
wwid
34
3600508b4000156d70001200000b0000
yellow
multibus
"round-robin 0"
manual
priorities
5
1DEC_____321816758474
⁠Chapt er 4 . T he DM- Mult ipat h Configurat ion File
alias
rr_weight
red
priorities
}
}
4 .5. Configurat ion File Devices
Table 4.3, “ D evice Attributes” shows the attributes that you can set for each individual storage device
in the d evi ces section of the mul ti path. co nf configuration file. These attributes are used by D MMultipath unless they are overwritten by the attributes specified in the mul ti paths section of the
mul ti path. co nf file for paths that contain the device. These attributes override the attributes set in
the d efaul ts section of the mul ti path. co nf file.
Many devices that support multipathing are included by default in a multipath configuration. The
values for the devices that are supported by default are listed in the mul ti path. co nf. d efaul ts
file. You probably will not need to modify the values for these devices, but if you do you can overwrite
the default values by including an entry in the configuration file for the device that overwrites those
values. You can copy the device configuration defaults from the mul ti path. co nf. d efaul ts file
for the device and override the values that you want to change.
To add a device that is not configured automatically by default to this section of the configuration
file, you need to set the vend o r and pro d uct parameters. You can find these values by looking at
/sys/bl o ck/device_name/d evi ce/vend o r and
/sys/bl o ck/device_name/d evi ce/mo d el where device_name is the device to be multipathed,
as in the following example:
# cat /sys/bl o ck/sd a/d evi ce/vend o r
WINSYS
# cat /sys/bl o ck/sd a/d evi ce/mo d el
SF2372
The additional parameters to specify depend on your specific device. If the device is active/active,
you will usually not need to set additional parameters. You may want to set
path_g ro upi ng _po l i cy to mul ti bus. Other parameters you may need to set are
no _path_retry and rr_mi n_i o , as described in Table 4.3, “ D evice Attributes” .
If the device is active/passive, but it automatically switches paths with I/O to the passive path, you
need to change the checker function to one that does not send I/O to the path to test if it is working
(otherwise, your device will keep failing over). This almost always means that you set the
path_checker to tur; this works for all SCSI devices that support the Test Unit Ready command,
which most do.
T ab le 4 .3. D evice At t rib u t es
At t rib u t e
vend o r
pro d uct
revi si o n
pro d uct_bl ackl i st
D escrip t io n
Specifies the vendor name of the storage device to which the
d evi ce attributes apply, for example C O MP AQ .
Specifies the product name of the storage device to which the
d evi ce attributes apply, for example HSV110 (C )C O MP AQ .
Specifies the product revision identifier of the storage device.
Specifies a regular expression used to blacklist devices by
product.
35
Red Hat Ent erprise Linux 6 DM Mult ipat h
At t rib u t e
hard ware_hand l er
D escrip t io n
Specifies a module that will be used to perform hardware specific
actions when switching path groups or handling I/O errors.
Possible values include:
1 emc: hardware handler for EMC storage arrays.
1 al ua: hardware handler for SCSI-3 ALUA arrays.
1 hp_sw: hardware handler for Compaq/HP controllers.
1 rd ac: hardware handler for the LSI/Engenio RD AC controllers.
path_g ro upi ng _po l i cy
Specifies the default path grouping policy to apply to unspecified
multipaths. Possible values include:
fai l o ver = 1 path per priority group
mul ti bus = all valid paths in 1 priority group
g ro up_by_seri al = 1 priority group per detected serial number
g ro up_by_pri o = 1 priority group per path priority value
g ro up_by_no d e_name = 1 priority group per target node name
g etui d _cal l o ut
Specifies the default program and arguments to call out to obtain
a unique path identifier. An absolute path is required.
path_sel ecto r
Specifies the default algorithm to use in determining what path to
use for the next I/O operation. Possible values include:
ro und -ro bi n 0 : Loop through every path in the path group,
sending the same amount of I/O to each.
q ueue-l eng th 0 : Send the next bunch of I/O down the path
with the least number of outstanding I/O requests.
servi ce-ti me 0 : Send the next bunch of I/O down the path
with the shortest estimated service time, which is determined by
dividing the total size of the outstanding I/O to each path by its
relative throughput.
36
⁠Chapt er 4 . T he DM- Mult ipat h Configurat ion File
At t rib u t e
path_checker
D escrip t io n
Specifies the default method used to determine the state of the
paths. Possible values include:
read secto r0 : Read the first sector of the device.
tur: Issue a T EST UNIT R EAD Y to the device.
emc_cl ari i o n: Query the EMC Clariion specific EVPD page
0xC0 to determine the path.
hp_sw: Check the path state for HP storage arrays with
Active/Standby firmware.
rd ac: Check the path stat for LSI/Engenio RD AC storage
controller.
d i recti o : Read the first sector with direct I/O.
features
The default extra features of multipath devices, using the format:
" number_of_features_plus_arguments feature1 ..." .
Possible values for features include:
q ueue_i f_no _path, which is the same as setting
no _path_retry to q ueue. For information on issues that may
arise when using this feature, see Section 5.6, “ Issues with
queue_if_no_path feature” .
retai n_attached _hw_hand l er: (Red Hat Enterprise Linux
Release 6.4 and later) If this parameter is set to yes and the scsi
layer has already attached a hardware handler to the path
device, multipath will not force the device to use the
hard ware_hand l er specified by the mul ti path. co nf file. If
the scsi layer has not attached a hardware handler, multipath will
continue to use its configured hardware handler as usual.
pg _i ni t_retri es n: Retry path group initialization up to n
times before failing where 1 <= n <= 50.
pg _i ni t_d el ay_msecs n: Wait n milliseconds between path
group initialization retries where 0 <= n <= 60000.
37
Red Hat Ent erprise Linux 6 DM Mult ipat h
At t rib u t e
pri o
D escrip t io n
Specifies the default function to call to obtain a path priority
value. For example, the ALUA bits in SPC-3 provide an
exploitable pri o value. Possible values include:
co nst: Set a priority of 1 to all paths.
emc: Generate the path priority for EMC arrays.
al ua: Generate the path priority based on the SCSI-3 ALUA
settings.
tpg _pref: Generate the path priority based on the SCSI-3 ALUA
settings, using the preferred port bit.
o ntap: Generate the path priority for NetApp arrays.
rd ac: Generate the path priority for LSI/Engenio RD AC controller.
hp_sw: Generate the path priority for Compaq/HP controller in
active/standby mode.
hd s: Generate the path priority for Hitachi HD S Modular storage
arrays.
fai l back
Manages path group failback.
A value of i mmed i ate specifies immediate failback to the highest
priority path group that contains active paths.
A value of manual specifies that there should not be immediate
failback but that failback can happen only with operator
intervention.
A value of fo l l o wo ver specifies that automatic failback should
be performed when the first path of a path group becomes active.
This keeps a node from automatically failing back when another
node requested the failover.
A numeric value greater than zero specifies deferred failback,
expressed in seconds.
rr_wei g ht
If set to pri o ri ti es, then instead of sending rr_mi n_i o
requests to a path before calling path_sel ecto r to choose the
next path, the number of requests to send is determined by
rr_mi n_i o times the path's priority, as determined by the pri o
function. If set to uni fo rm, all path weights are equal.
no _path_retry
A numeric value for this attribute specifies the number of times the
system should attempt to use a failed path before disabling
queueing.
A value of fai l indicates immediate failure, without queueing.
A value of q ueue indicates that queueing should not stop until
the path is fixed.
38
⁠Chapt er 4 . T he DM- Mult ipat h Configurat ion File
At t rib u t e
rr_mi n_i o
rr_mi n_i o _rq
fast_i o _fai l _tmo
d ev_l o ss_tmo
fl ush_o n_l ast_d el
user_fri end l y_names
retai n_attached _hw_han
d l er
d etect_pri o
D escrip t io n
Specifies the number of I/O requests to route to a path before
switching to the next path in the current path group. This setting
is only for systems running kernels older that 2.6.31. Newer
systems should use rr_mi n_i o _rq . The default value is 1000.
Specifies the number of I/O requests to route to a path before
switching to the next path in the current path group, using
request-based device-mapper-multipath. This setting should be
used on systems running current kernels. On systems running
kernels older than 2.6.31, use rr_mi n_i o . The default value is 1.
The number of seconds the SCSI layer will wait after a problem
has been detected on an FC remote port before failing I/O to
devices on that remote port. This value should be smaller than
the value of d ev_l o ss_tmo . Setting this to o ff will disable the
timeout.
The number of seconds the SCSI layer will wait after a problem
has been detected on an FC remote port before removing it from
the system. Setting this to infinity will set this to 2147483647
seconds,or 68 years.
If set to yes, the mul ti pathd daemon will disable queueing
when the last path to a device has been deleted.
If set to yes, specifies that the system should use the
/etc/mul ti path/bi nd i ng s file to assign a persistent and
unique alias to the multipath, in the form of mpathn. If set to no ,
specifies that the system should use use the WWID as the alias
for the multipath. In either case, what is specified here will be
overridden by any device-specific aliases you specify in the
mul ti paths section of the configuration file. The default value is
no .
(Red Hat Enterprise Linux Release 6.4 and later) If this parameter
is set to yes and the scsi layer has already attached a hardware
handler to the path device, multipath will not force the device to
use the hard ware_hand l er specified by the mul ti path. co nf
file. If the scsi layer has not attached a hardware handler,
multipath will continue to use its configured hardware handler as
usual.
(Red Hat Enterprise Linux Release 6.4 and later) If this is set to
yes, multipath will first check if the device supports ALUA, and if
so it will automatically assign the device the al ua prioritizer. If
the device doesn't support ALUA, it will determine the prioritizer as
it always does.
The following example shows a d evi ce entry in the multipath configuration file.
# }
# device {
# vendor
"COMPAQ "
# product
"MSA1000
"
# path_grouping_policy multibus
# path_checker tur
# rr_weight priorities
# }
#}
39
Red Hat Ent erprise Linux 6 DM Mult ipat h
Chapter 5. DM-Multipath Administration and Troubleshooting
This chapter will provide information on administering D M-Multipath on a running system. It includes
sections on the following topics:
Resizing an online multipath device
Moving the root device from a single-path device to a multipath device
Moving the swap device from a single path device to a multipath device
The multipath daemon
Issues with large number of LUNs
Issues with queue_if_no_path feature
mul ti path command output
Multipath queries with the mul ti path command
mul ti path command options
Multipath queries with the d msetup command
Troubleshooting with the mul ti pathd interactive console
5.1. Resiz ing an Online Mult ipat h Device
If you need to resize an online multipath device, use the following procedure.
1. Resize your physical device.
2. Execute the following command to find the paths to the LUN:
# mul ti path -l
3. Resize your paths. For SCSI devices, writing a 1 to the rescan file for the device causes the
SCSI driver to rescan, as in the following command:
# echo 1 > /sys/bl o ck/device_name/d evi ce/rescan
4. Resize your multipath device by executing the mul ti pathd resi ze command:
# mul ti pathd -k' resi ze map mpatha'
5. Resize the file system (assuming no LVM or D OS partitions are used):
# resi ze2fs /d ev/mapper/mpatha
5.2. Moving root File Syst ems from a Single Pat h Device t o a Mult ipat h
Device
40
⁠Chapt er 5. DM- Mult ipat h Administ rat ion and T roubleshoot ing
If you have installed your system on a single-path device and later add another path to the root file
system, you will need to move your root file system to a multipathed device. This section documents
the procedure for moving from a single-path to a multipathed device.
After ensuring that you have installed the d evi ce-mapper-mul ti path package, perform the
following procedure:
1. Execute the following command to create the /etc/mul ti path. co nf configuration file,
load the multipath module, and set chkco nfi g for the mul ti pathd to o n:
# mpathco nf --enabl e
For further information on using the mpathco nf command to set up multipathing, see
Section 3.1, “ Setting Up D M-Multipath” .
2. Edit the bl ackl i st and bl ackl i st_excepti o ns sections of the
/etc/mul ti path. co nf file, as described in Section 4.2, “ Configuration File Blacklist” .
3. To confirm that your configuration file is set up correctly, you can run the /sbi n/mul ti path
command with the -v3 option to check whether the multipath daemon tried to create a
multipath device over your root device. The command will fail since the root the device is in
use, but the output from the command should show the root device in the paths list.
You should look in the command output for a line of the following format:
WWID
H:B:T:L devname MAJOR:MINOR
For example, if your root file system is set up on sd a or one of its partitions, you would see a
line in the output such as the following:
===== paths list =====
...
1ATA
WDC WD800JD-75MSA3
1:0:0:0 sda 8:0
...
WD-WMAM9F
Later in the output, you should see the root device assigned to a multipath device:
time | devname: ownership set to mpathdev
For example, the output may appear as follows:
Jun 14 06:48:21 | sda: ownership set to mpatha
You will also see an indication that the command failed to create the multipath device with a
line of the following format:
time | mpathdev: domap (0) failure for create/reload map
In the example noted above, you would see the following line in the command output:
Jun 14 06:48:21 | mpatha: domap (0) failure for create/reload map
41
Red Hat Ent erprise Linux 6 DM Mult ipat h
4. To rebuild the i ni tramfs file system with mul ti path, execute the d racut command with
the following options:
# d racut --fo rce --ad d mul ti path --i ncl ud e /etc/mul ti path
/etc/mul ti path
5. If your root device is not an LVM volume and it is mounted by device name, you may need to
edit the fstab file to switch to the appropriate multipath device name. If your root device is an
LVM device or is mounted by UUID or something else, this step is not necessary.
a. Use the procedure described in Step 3 of running the /sbi n/mul ti path command
with the -v3 to determine the WWID of the root device.
b. Set up an alias for the root device in the /etc/mul ti path. co nf file:
multipaths {
multipath {
wwid WWID_of_root_device
alias rootdev
}
}
c. Edit the /etc/fstab and replace the old device path to the root device with the
multipath device.
For example, if you had the following entry in the /etc/fstab file:
/dev/sda1 /
ext4
defaults
1 1
ext4
defaults
1 1
You would change the entry to the following:
/dev/mapper/rootdev /
If you need to edit the /etc/fstab file, you will also need to edit the
/etc/g rub/g rub. co nf file and change the root parameter from ro o t= /d ev/sd a1 to
ro o t= /d ev/mapper/ro o td ev.
The following example shows what this g rub. co nf file entry would look like before you edit
it.
title Red Hat Enterprise Linux FoundationServer (2.6.3271.24.1.el6.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.32-71.24.1.el6.x86_64 ro root=/dev/sda1
rd_NO_LUKS
rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16
KEYTABLE=us
console=ttyS0,115200n8 crashkernel=auto
initrd /initramfs-2.6.32-71.24.1.el6.x86_64.img
The following example shows what the g rub. co nf file entry would look like after you edit it.
title Red Hat Enterprise Linux FoundationServer (2.6.3271.24.1.el6.x86_64)
root (hd0,0)
42
⁠Chapt er 5. DM- Mult ipat h Administ rat ion and T roubleshoot ing
kernel /vmlinuz-2.6.32-71.24.1.el6.x86_64 ro
root=/dev/mapper/rootdev
rd_NO_LUKS rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrhebsun16
KEYTABLE=us console=ttyS0,115200n8 crashkernel=auto
initrd /initramfs-2.6.32-71.24.1.el6.x86_64.img
6. Shut the machine down.
7. Configure the FC switch so that other paths are visible to the machine.
8. Boot the machine.
9. Check whether the root file system ('/') is on the multipathed device.
5.3. Moving swap File Syst ems from a Single Pat h Device t o a Mult ipat h
Device
By default, swap devices are set up as logical volumes. This does not require any special procedure
for configuring them as multipath devices as long as you set up multipathing on the physical
volumes that constitute the logical volume group. If your swap device is not an LVM volume, however,
and it is mounted by device name, you may need to edit the fstab file to switch to the appropriate
multipath device name.
1. D etermine the WWID number of the swap device by running the /sbi n/mul ti path
command with the -v3 option. The output from the command should show the swap device in
the paths list.
You should look in the command output for a line of the following format, showing the swap
device:
WWID
H:B:T:L devname MAJOR:MINOR
For example, if your swap file system is set up on sd a or one of its partitions, you would see a
line in the output such as the following:
===== paths list =====
...
1ATA
WDC WD800JD-75MSA3
1:0:0:0 sda 8:0
...
WD-WMAM9F
2. Set up an alias for the swap device in the /etc/mul ti path. co nf file:
multipaths {
multipath {
wwid WWID_of_swap_device
alias swapdev
}
}
3. Edit the /etc/fstab and replace the old device path to the root device with the multipath
device.
For example, if you had the following entry in the /etc/fstab file:
43
Red Hat Ent erprise Linux 6 DM Mult ipat h
/dev/sda2 swap
ext4
defaults
0 0
ext4
defaults
0 0
You would change the entry to the following:
/dev/mapper/swapdev swap
5.4 . T he Mult ipat h Daemon
If you find you have trouble implementing a multipath configuration, you should ensure that the
multipath daemon is running, as described in Chapter 3, Setting Up DM-Multipath. The mul ti pathd
daemon must be running in order to use multipathed devices.
5.5. Issues wit h Large Number of LUNs
When a large number of LUNs are added to a node, using multipathed devices can significantly
increase the time it takes for the ud ev device manager to create device nodes for them. If you
experience this problem, you can correct it by deleting the following line in
/etc/ud ev/rul es. d /4 0 -mul ti path. rul es:
KERNEL!="dm-[0-9]*", ACTION=="add", PROGRAM=="/bin/bash -c '/sbin/lsmod |
/bin/grep ^dm_multipath'", RUN+="/sbin/multipath -v0 %M:%m"
This line causes the ud ev device manager to run mul ti path every time a block device is added to
the node. Even with this line removed, the mul ti pathd daemon will still automatically create
multipathed devices, and mul ti path will still be called during the boot process for nodes with
multipathed root file systems. The only change is that multipathed devices will not be automatically
created when the mul ti pathd daemon is not running, which should not be a problem for the vast
majority of multipath users.
5.6. Issues wit h queue_if_no_pat h feat ure
If features "1 q ueue_i f_no _path" is specified in the /etc/mul ti path. co nf file, then any
process that issues I/O will hang until one or more paths are restored. To avoid this, set the
no _path_retry N parameter in the /etc/mul ti path. co nf file (where N is the number of times the
system should retry a path).
When you set the no _path_retry parameter, remove the features "1 q ueue_i f_no _path"
option from the /etc/mul ti path. co nf file as well. If, however, you are using a multipathed device
for which the features "1 q ueue_i f_no _path" option is set as a compiled-in default, as it is for
many SAN devices, you must explicitly add features "0 " to override this default. You can do this
by copying the existing devices section for your device from /usr/share/d o c/d evi ce-mappermul ti path-0 . 4 . 9 /mul ti path. co nf. d efaul ts into /etc/mul ti path. co nf and editing it to
suit your needs.
If you need to use the features "1 q ueue_i f_no _path" option and you experience the issue
noted here, use the d msetup command to edit the policy at runtime for a particular LUN (that is, for
which all the paths are unavailable). For example, if you want to change the policy on the multipath
device mpathc from "q ueue_i f_no _path" to "fai l _i f_no _path", execute the following
command.
dmsetup message mpathc 0 "fail_if_no_path"
44
⁠Chapt er 5. DM- Mult ipat h Administ rat ion and T roubleshoot ing
Note that you must specify the mpathn alias rather than the path.
5.7. Mult ipat h Command Out put
When you create, modify, or list a multipath device, you get a display of the current device setup. The
format is as follows.
For each multipath device:
action_if_any: alias (wwid_if_different_from_alias)
dm_device_name_if_known vendor,product size=size features='features'
hwhandler='hardware_handler' wp=write_permission_if_known
For each path group:
-+- policy='scheduling_policy' prio=prio_if_known
status=path_group_status_if_known
For each path:
`- host:channel:id:lun devnode major:minor dm_status_if_known
path_status online_status
For example, the output of a multipath command might appear as follows:
3600d0230000000000e13955cc3757800 dm-1 WINSYS,SF2372
size=269G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=active
| `- 6:0:0:0 sdb 8:16 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
`- 7:0:0:0 sdf 8:80 active ready running
If the path is up and ready for I/O, the status of the path is read y or g ho st. If the path is down, the
status is faul ty or shaky. The path status is updated periodically by the mul ti pathd daemon
based on the polling interval defined in the /etc/mul ti path. co nf file.
The dm status is similar to the path status, but from the kernel's point of view. The dm status has two
states: fai l ed , which is analogous to faul ty, and acti ve which covers all other path states.
Occasionally, the path state and the dm state of a device will temporarily not agree.
The possible values for online_status are runni ng and o ffl i ne. A status of o ffl i ne means
that this SCSI device has been disabled.
Note
When a multipath device is being created or modified, the path group status, the dm device
name, the write permissions, and the dm status are not known. Also, the features are not
always correct.
5.8. Mult ipat h Queries wit h mult ipat h Command
45
Red Hat Ent erprise Linux 6 DM Mult ipat h
You can use the -l and -l l options of the mul ti path command to display the current multipath
configuration. The -l option displays multipath topology gathered from information in sysfs and
the device mapper. The -l l option displays the information the -l displays in addition to all other
available components of the system.
When displaying the multipath configuration, there are three verbosity levels you can specify with the
-v option of the mul ti path command. Specifying -v0 yields no output. Specifying -v1 outputs the
created or updated multipath names only, which you can then feed to other tools such as kpartx.
Specifying -v2 prints all detected paths, multipaths, and device maps.
The following example shows the output of a mul ti path -l command.
# mul ti path -l
3600d0230000000000e13955cc3757800 dm-1 WINSYS,SF2372
size=269G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=active
| `- 6:0:0:0 sdb 8:16 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
`- 7:0:0:0 sdf 8:80 active ready running
The following example shows the output of a mul ti path -l l command.
# mul ti path -l l
3600d0230000000000e13955cc3757801 dm-10 WINSYS,SF2372
size=269G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=enabled
| `- 19:0:0:1 sdc 8:32 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
`- 18:0:0:1 sdh 8:112 active ready running
3600d0230000000000e13955cc3757803 dm-2 WINSYS,SF2372
size=125G features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
|- 19:0:0:3 sde 8:64 active ready running
`- 18:0:0:3 sdj 8:144 active ready running
5.9. Mult ipat h Command Opt ions
Table 5.1, “ Useful mul ti path Command Options” describes some options of the mul ti path
command that you may find useful.
T ab le 5.1. U sef u l mul ti path C o mman d O p t io n s
O p t io n
D escrip t io n
-l
D isplay the current multipath configuration gathered from sysfs and
the device mapper.
D isplay the current multipath configuration gathered from sysfs, the
device mapper, and all other available components on the system.
Remove the named multipath device.
Remove all unused multipath devices.
(Red Hat Enterprise Linux 6.6 and later) Remove the wwi d of the
specified device from the wwi d s file.
(Red Hat Enterprise Linux 6.6 and later) Reset the wwi d s file to
include only the current multipath devices.
-l l
-f device
-F
-w device
-W
46
⁠Chapt er 5. DM- Mult ipat h Administ rat ion and T roubleshoot ing
5.10. Det ermining Device Mapper Ent ries wit h t he dmset up Command
You can use the d msetup command to find out which device mapper entries match the multipathed
devices.
The following command displays all the device mapper devices and their major and minor numbers.
The minor numbers determine the name of the dm device. For example, a minor number of 3
corresponds to the multipathed device /d ev/d m-3.
# d msetup l s
mpathd (253:4)
mpathep1
(253:12)
mpathfp1
(253:11)
mpathb (253:3)
mpathgp1
(253:14)
mpathhp1
(253:13)
mpatha (253:2)
mpathh (253:9)
mpathg (253:8)
VolGroup00-LogVol01
(253:1)
mpathf (253:7)
VolGroup00-LogVol00
(253:0)
mpathe (253:6)
mpathbp1
(253:10)
mpathd (253:5)
5.11. T roubleshoot ing wit h t he mult ipat hd Int eract ive Console
The mul ti pathd -k command is an interactive interface to the mul ti pathd daemon. Executing
this command brings up an interactive multipath console. After executing this command, you can
enter hel p to get a list of available commands, you can enter an interactive command, or you can
enter C T R L-D to quit.
The mul ti pathd interactive console can be used to troubleshoot problems you may be having with
your system. For example, the following command sequence displays the multipath configuration,
including the defaults, before exiting the console.
# mul ti pathd -k
> > sho w co nfi g
> > C T R L-D
The following command sequence ensures that multipath has picked up any changes to the
mul ti path. co nf,
# mul ti pathd -k
> > reco nfi g ure
> > C T R L-D
Use the following command sequence to ensure that the path checker is working properly.
# mul ti pathd -k
> > sho w paths
> > C T R L-D
47
Red Hat Ent erprise Linux 6 DM Mult ipat h
48
Revision Hist ory
Revision History
R evisio n 7.0- 4
Version for 6.6 GA release
T h u Au g 7 2014
St even Levin e
R evisio n 7.0- 3
Version for 6.6 Beta release
T h u Au g 7 2014
St even Levin e
R evisio n 7.0- 1
Mo n Ju l 7 2014
St even Levin e
Resolves: #1117038
D ocuments new -w and -W options of the mul ti path command.
Resolves: #1116946
D ocuments all possible values of features entry in mul ti path. co nf file.
Resolves: #969080
Small editorial clarifications.
Resolves: #1081264
D ocuments fo rce_sync parameter.
R evisio n 6 .0- 7
Wed Ap r 10 2014
Administrative Update to fix Review Server Beta build
St even Levin e
R evisio n 6 .0- 6
Version for 6.5 GA release
Wed N o v 13 2013
St even Levin e
R evisio n 6 .0- 5
Version for 6.5 Beta release
Fri Sep 27 2013
St even Levin e
R evisio n 6 .0- 3
Fri Sep 27 2013
St even Levin e
Resolves: #987144, #987671
D ocuments new rel o ad _rewri te and repl ace_wwi d _whi tespace parameters in the
mul ti path. co nf file.
Resolves: #911630, #969022
Corrects small typographical errors.
R evisio n 6 .0- 1
T u e Sep 10 2013
Adding new default parameters for RHEL 6.5.
St even Levin e
R evisio n 5.0- 9
Version for 6.4 GA release
Mo n Feb 18 2013
St even Levin e
R evisio n 5.0- 7
Version for 6.4 Beta release
Mo n N o v 26 2012
St even Levin e
R evisio n 5.0- 6
T u e N o v 13 2012
St even Levin e
49
Red Hat Ent erprise Linux 6 DM Mult ipat h
Resolves: #856829
D ocuments new retai n_attached _hard ware_hand l er and d etect_pri o configuration
parameters.
Resolves: #815925
D ocuments the procedure for setting up multipathing in the i ni tramfs file system.
Resolves: #836333
Corrects small typographical error.
Resolves: #856826
Updates sample mul ti path. co nf excerpt to reflect updated path_sel ecto r parameter.
R evisio n 4 .0- 3
Version for 6.3 GA release
Fri Ju n 15 2012
St even Levin e
R evisio n 4 .0- 2
Wed Ap r 25 2012
Resolves: #815925
Updates output format for d msetup l s example.
St even Levin e
R evisio n 4 .0- 1
Wed Mar 28 2012
Resolves: #786399
Fixes small typographic error.
St even Levin e
Resolves: #771420
D ocuments new D M-Multipath features for Red Hat Enterprise Linux 6.3.
R evisio n 3.0- 3
T h u D ec 1 2011
Release for GA of Red Hat Enterprise Linux 6.2
St even Levin e
Resolves: #753899
Corrects description of mul ti path -F option.
R evisio n 3.0- 2
Fri O ct 7 2011
Resolves: #743767
Fixes typos and clarifies small issues.
St even Levin e
R evisio n 3.0- 1
Mo n Sep 19 2011
Initial revision for Red Hat Enterprise Linux 6.2 Beta release
St even Levin e
Resolves: #707638
D ocuments new D M-Multipath features for Red Hat Enterprise Linux 6.2.
Resolves: #715457
Corrects filter example for SCSI devices.
Resolves: #623450
Updates procedures for moving root device to a multipathed volume.
Resolves: #725374, #738051
Corrects minor typographical errors.
50
⁠Index
R evisio n 2.0- 1
T h u May 19 2011
Initial revision for Red Hat Enterprise Linux 6.1
St even Levin e
Resolves: #623450
Adds new procedures for moving root and swap devices from single path to multipathed devices.
Resolves: #693948
Corrects small errors in tables of device attributes.
Resolves: #694683
Corrects small typographic errors.
Resolves: #702721
Removes outdated reference to /dev/mpath.
R evisio n 1.0- 1
Wed N o v 10 2010
First version for the Red Hat Enterprise Linux 6 release
St even Levin e
Index
Symbols
/et c/mu lt ip at h .co n f p ackag e, Set t in g U p D M- Mu lt ip at h
A
act ive/act ive co n f ig u rat io n
- definition, Overview of D M-Multipath
- illustration, Overview of D M-Multipath
act ive/p assive co n f ig u rat io n
- definition, Overview of D M-Multipath
- illustration, Overview of D M-Multipath
alias p aramet er , Mu lt ip at h s D evice C o n f ig u rat io n At t rib u t es
- configuration file, Multipath D evice Identifiers
B
b lacklist
-
configuration file, Configuration File Blacklist
default devices, Blacklisting By D evice Name
device name, Blacklisting By D evice Name
device type, Blacklisting By D evice Type
WWID , Blacklisting by WWID
b lacklist _excep t io n s sect io n
- multipath.conf file, Blacklist Exceptions
C
ch ecker_t imeo u t p aramet er, C o n f ig u rat io n File D ef au lt s
co n f ig u rat io n f ile
- alias parameter, Multipaths D evice Configuration Attributes
- blacklist, Configuration File Blacklist
51
Red Hat Ent erprise Linux 6 DM Mult ipat h
- checker_timeout parameter, Configuration File D efaults
- detect_prio parameter, Configuration File D efaults, Multipaths D evice Configuration
Attributes
- dev_loss_tmo parameter, Configuration File D efaults, Configuration File D evices
- failback parameter, Configuration File D efaults, Multipaths D evice Configuration
Attributes, Configuration File D evices
- fast_io_fail_tmo parameter, Configuration File D efaults, Configuration File D evices
- features parameter, Configuration File D efaults, Configuration File D evices
- flush_on_last_del parameter, Configuration File D efaults, Multipaths D evice
Configuration Attributes, Configuration File D evices
- force_sync parameter, Configuration File D efaults
- getuid_callout parameter, Configuration File D efaults, Configuration File D evices
- hardware_handler parameter, Configuration File D evices
- hwtable_regex_match parameter, Configuration File D efaults
- max_fds parameter, Configuration File D efaults
- no_path_retry parameter, Configuration File D efaults, Multipaths D evice
Configuration Attributes, Configuration File D evices
- overview, Configuration File Overview
- path_checker parameter, Configuration File D efaults, Configuration File D evices
- path_grouping_policy parameter, Configuration File D efaults, Multipaths D evice
Configuration Attributes, Configuration File D evices
- path_selector parameter, Configuration File D efaults, Multipaths D evice
Configuration Attributes, Configuration File D evices
- polling-interval parameter, Configuration File D efaults
- prio parameter, Configuration File D efaults, Configuration File D evices
- product parameter, Configuration File D evices
- product_blacklist parameter, Configuration File D evices
- queue_without_daemon parameter, Configuration File D efaults
- retain_attached_hw_handler parameter, Configuration File D efaults, Multipaths
D evice Configuration Attributes
- revision parameter, Configuration File D evices
- rr_min_io parameter, Configuration File D efaults, Multipaths D evice Configuration
Attributes
- rr_weight parameter, Configuration File D efaults, Multipaths D evice Configuration
Attributes, Configuration File D evices
- udev_dir parameter, Configuration File D efaults
- user_friendly_names parameter, Configuration File D efaults, Multipaths D evice
Configuration Attributes, Configuration File D evices
- vendor parameter, Configuration File D evices
- verbosity parameter, Configuration File D efaults
- wwid parameter, Multipaths D evice Configuration Attributes
co n f ig u rin g
- D M-Multipath, Setting Up D M-Multipath
D
d ef au lt s sect io n
- multipath.conf file, Configuration File D efaults
d et ect _p rio p aramet er, C o n f ig u rat io n File D ef au lt s, Mu lt ip at h s D evice
C o n f ig u rat io n At t rib u t es
d ev/map p er d irect o ry, Mu lt ip at h D evice Id en t if iers
d evice n ame, Mu lt ip at h D evice Id en t if iers
d evice- map p er- mu lt ip at h p ackag e, Set t in g U p D M- Mu lt ip at h
52
⁠Index
d evices
- adding, Configuring Storage D evices, Configuration File D evices
d evices sect io n
- multipath.conf file, Configuration File D evices
d ev_lo ss_t mo p aramet er, C o n f ig u rat io n File D ef au lt s, C o n f ig u rat io n File D evices
D M- Mu lt ip at h
- and LVM, Multipath D evices in Logical Volumes
- components, D M-Multipath Components
- configuration file, The D M-Multipath Configuration File
- configuring, Setting Up D M-Multipath
- definition, D evice Mapper Multipathing
- device name, Multipath D evice Identifiers
- devices, Multipath D evices
- failover, Overview of D M-Multipath
- overview, Overview of D M-Multipath
- redundancy, Overview of D M-Multipath
- setup, Setting Up D M-Multipath
- setup, overview, D M-Multipath Setup Overview
d m- n d evices, Mu lt ip at h D evice Id en t if iers
d mset u p co mman d , d et ermin in g d evice map p er en t ries, D et ermin in g D evice
Map p er En t ries wit h t h e d mset u p C o mman d
d m_mu lt ip at h kern el mo d u le , D M- Mu lt ip at h C o mp o n en t s
F
f ailb ack p aramet er, C o n f ig u rat io n File D ef au lt s, Mu lt ip at h s D evice C o n f ig u rat io n
At t rib u t es, C o n f ig u rat io n File D evices
f ailo ver, O verview o f D M- Mu lt ip at h
f ast _io _f ail_t mo p aramet er, C o n f ig u rat io n File D ef au lt s, C o n f ig u rat io n File
D evices
f eat u res p aramet er, C o n f ig u rat io n File D ef au lt s, C o n f ig u rat io n File D evices
f eat u res, n ew an d ch an g ed , N ew an d C h an g ed Feat u res
f eed b ack
- contact information for this manual, We Need Feedback!
f lu sh _o n _last _d el p aramet er, C o n f ig u rat io n File D ef au lt s, Mu lt ip at h s D evice
C o n f ig u rat io n At t rib u t es, C o n f ig u rat io n File D evices
f o rce_syn c p aramet er, C o n f ig u rat io n File D ef au lt s
G
g et u id _callo u t p aramet er, C o n f ig u rat io n File D ef au lt s, C o n f ig u rat io n File D evices
H
h ard ware_h an d ler p aramet er, C o n f ig u rat io n File D evices
h wt ab le_reg ex_mat ch p aramet er, C o n f ig u rat io n File D ef au lt s
I
in it ramf s
- starting multipath, Setting Up Multipathing in the initramfs File System
53
Red Hat Ent erprise Linux 6 DM Mult ipat h
K
kp art x co mman d , D M- Mu lt ip at h C o mp o n en t s
L
lo cal d isks, ig n o rin g , Ig n o rin g Lo cal D isks wh en G en erat in g Mu lt ip at h D evices
LVM p h ysical vo lu mes
- multipath devices, Multipath D evices in Logical Volumes
lvm.co n f f ile , Mu lt ip at h D evices in Lo g ical Vo lu mes
M
max_f d s p aramet er, C o n f ig u rat io n File D ef au lt s
mp at h co n f co mman d , D M- Mu lt ip at h C o mp o n en t s
mu lt ip at h co mman d , D M- Mu lt ip at h C o mp o n en t s
- options, Multipath Command Options
- output, Multipath Command Output
- queries, Multipath Queries with multipath Command
mu lt ip at h d aemo n ( mu lt ip at h d ) , T h e Mu lt ip at h D aemo n
mu lt ip at h d evices, Mu lt ip at h D evices
- logical volumes, Multipath D evices in Logical Volumes
- LVM physical volumes, Multipath D evices in Logical Volumes
mu lt ip at h .co n f f ile, St o rag e Array Su p p o rt , T h e D M- Mu lt ip at h C o n f ig u rat io n File
- blacklist_exceptions section, Blacklist Exceptions
- defaults section, Configuration File D efaults
- devices section, Configuration File D evices
- multipaths section, Multipaths D evice Configuration Attributes
mu lt ip at h .co n f .an n o t at ed f ile, T h e D M- Mu lt ip at h C o n f ig u rat io n File
mu lt ip at h .co n f .d ef au lt s f ile, St o rag e Array Su p p o rt , T h e D M- Mu lt ip at h
C o n f ig u rat io n File
mu lt ip at h d
- command, Troubleshooting with the multipathd Interactive Console
- interactive console, Troubleshooting with the multipathd Interactive Console
mu lt ip at h d d aemo n , D M- Mu lt ip at h C o mp o n en t s
mu lt ip at h d st art co mman d , Set t in g U p D M- Mu lt ip at h
mu lt ip at h ed ro o t f ile syst em, Mo vin g ro o t File Syst ems f ro m a Sin g le Pat h D evice t o
a Mu lt ip at h D evice
mu lt ip at h ed swap f ile syst em, Mo vin g swap File Syst ems f ro m a Sin g le Pat h D evice
t o a Mu lt ip at h D evice
mu lt ip at h s sect io n
- multipath.conf file, Multipaths D evice Configuration Attributes
N
n o _p at h _ret ry p aramet er, C o n f ig u rat io n File D ef au lt s, Mu lt ip at h s D evice
C o n f ig u rat io n At t rib u t es, C o n f ig u rat io n File D evices
O
54
⁠Index
o verview
- features, new and changed, New and Changed Features
P
p at h _ch ecker p aramet er, C o n f ig u rat io n File D ef au lt s, C o n f ig u rat io n File D evices
p at h _g ro u p in g _p o licy p aramet er, C o n f ig u rat io n File D ef au lt s, Mu lt ip at h s D evice
C o n f ig u rat io n At t rib u t es, C o n f ig u rat io n File D evices
p at h _select o r p aramet er, C o n f ig u rat io n File D ef au lt s, Mu lt ip at h s D evice
C o n f ig u rat io n At t rib u t es, C o n f ig u rat io n File D evices
p o llin g _in t erval p aramet er, C o n f ig u rat io n File D ef au lt s
p rio p aramet er, C o n f ig u rat io n File D ef au lt s, C o n f ig u rat io n File D evices
p ro d u ct p aramet er, C o n f ig u rat io n File D evices
p ro d u ct _b lacklist p aramet er, C o n f ig u rat io n File D evices
Q
q u eu e_wit h o u t _d aemo n p aramet er, C o n f ig u rat io n File D ef au lt s
R
resiz in g a mu lt ip at h d evice, R esiz in g an O n lin e Mu lt ip at h D evice
ret ain _at t ach ed _h w_h an d ler p aramet er, C o n f ig u rat io n File D ef au lt s, Mu lt ip at h s
D evice C o n f ig u rat io n At t rib u t es
revisio n p aramet er, C o n f ig u rat io n File D evices
ro o t f ile syst em, Mo vin g ro o t File Syst ems f ro m a Sin g le Pat h D evice t o a Mu lt ip at h
D evice
rr_min _io p aramet er, C o n f ig u rat io n File D ef au lt s, Mu lt ip at h s D evice C o n f ig u rat io n
At t rib u t es
rr_weig h t p aramet er, C o n f ig u rat io n File D ef au lt s, Mu lt ip at h s D evice C o n f ig u rat io n
At t rib u t es, C o n f ig u rat io n File D evices
S
set u p
- D M-Multipath, Setting Up D M-Multipath
st o rag e array su p p o rt , St o rag e Array Su p p o rt
st o rag e arrays
- adding, Configuring Storage D evices, Configuration File D evices
swap f ile syst em, Mo vin g swap File Syst ems f ro m a Sin g le Pat h D evice t o a
Mu lt ip at h D evice
U
u d ev_d ir p aramet er, C o n f ig u rat io n File D ef au lt s
u ser_f rien d ly_n ames p aramet er , Mu lt ip at h D evice Id en t if iers, C o n f ig u rat io n File
D ef au lt s, Mu lt ip at h s D evice C o n f ig u rat io n At t rib u t es, C o n f ig u rat io n File D evices
V
ven d o r p aramet er, C o n f ig u rat io n File D evices
verb o sit y p aramet er, C o n f ig u rat io n File D ef au lt s
55
Red Hat Ent erprise Linux 6 DM Mult ipat h
W
Wo rld Wid e Id en t if ier ( WWID ) , Mu lt ip at h D evice Id en t if iers
wwid p aramet er, Mu lt ip at h s D evice C o n f ig u rat io n At t rib u t es
56
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