Using Switches with a PS Series Group

Cisco® Catalyst 3750 and 2970 Switches
Using Switches with a PS Series Group
Abstract
This Technical Report describes how to
use Cisco Catalyst 3750 and 2970
switches with a
PS Series group to create a high
performance and highly available iSCSI
SAN.
Copyright © 2005 EqualLogic, Inc.
April 2005
EqualLogic is a registered trademark of EqualLogic, Inc.
All trademarks and registered trademarks mentioned herein are the property of their respective owners.
Possession, use, or copying of the documentation or the software described in this publication is authorized
only under the license agreement specified herein.
EqualLogic, Inc. will not be held liable for technical or editorial errors or omissions contained herein. The
information in this document is subject to change. Your performance can vary.
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Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
Table of Contents
Technical Report Revision Information .................................................................................1
Cisco Revision Information ...................................................................................................1
Introduction ............................................................................................................................1
Basic Steps .............................................................................................................................2
Understanding Switch and Server Recommendations ...........................................................3
Spanning-Tree ....................................................................................................................3
Flow Control .......................................................................................................................4
Unicast Storm Control ........................................................................................................5
Jumbo Frames .....................................................................................................................5
VLANs ...............................................................................................................................6
Catalyst 3750 and 2970 Switch Configuration ......................................................................6
Cisco Switch Interfaces ......................................................................................................7
Enabling the PortFast Option to Configure STP Edge Ports ..............................................7
Configuring Flow Control ..................................................................................................8
Disabling Unicast Storm Control .......................................................................................9
Configuring Jumbo Frames ................................................................................................9
Documentation and Customer Support ................................................................................11
Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
iii
Technical Report Revision Information
The following table describes the release history of this Technical Report.
Technical Report Revision Date
Change
1.0
Initial release.
4/19/2005
Cisco Revision Information
The following table shows the Cisco 3750 and 2970 Series switch software versions used for the
preparation of this Technical Report.
Vendor
Model
Software Revision
Software Image
Cisco
WS-C3750G-24TS
12.2(20)SE4
C3750-I9-M
Cisco
WS-C2970G-24T-E
12.1(19)EA1d
C2970-I6L2-M
Introduction
This Technical Report describes how to use Cisco Catalyst 3750 and 2970 switches with a PS
Series group to create a high-performance and highly-available iSCSI SAN.
The Cisco Catalyst 3750 switch is an innovative product that can be used in a SAN to provide
highly scalable network connectivity. Featuring Cisco StackWise™ technology, the switch
improves SAN efficiency by combining ease-of-use, scalability, and the highest resiliency
available for stackable switches.
Cisco Catalyst 2970 switches are affordable Gigabit Ethernet switches that deliver wire-speed,
intelligent services for small and medium businesses and enterprise branch offices. Featuring a
complete set of services, the Catalyst 2970 switches can enhance network performance and
increase productivity for today's knowledge workers by intelligently scaling beyond 100 Mbps over
existing Category 5 copper cabling.
EqualLogic storage solutions offer a fundamental change in iSCSI SAN implementation. By
configuring PS Series storage arrays into a PS Series group, both large and small businesses can
incrementally deploy a modular and affordable iSCSI SAN solution that easily scales to hundreds
of terabytes.
Built on ground-breaking, patented architecture, PS Series storage arrays deliver enterprise-quality
performance and reliability for all major operating systems. Intelligent automation and seamless
virtualization of a single pool of group storage greatly simplify storage management. PS Series
storage arrays also provide a comprehensive set of high-level features, in addition to fully
redundant, hot-swappable hardware.
Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
1
Figure 1: PS Series Storage Array
Use the recommendations in this Technical Report for proper connectivity and configuration of
Cisco Catalyst 3750 and 2970 switches and PS Series storage arrays to dramatically improve iSCSI
SAN performance and data availability.
Basic Steps
Follow these recommended basic steps to use Cisco Catalyst 3750 and 2970 switches with
PS Series storage arrays to create a high-performance and highly-available iSCSI SAN:
1. Set up a PS Series group and create volumes in the group. See the PS Series QuickStart or
Group Administration manual for information. Also, see the Network Connection and
Performance Guidelines Technical Report on the EqualLogic Customer Support website for
detailed information about how to improve performance when using a PS Series group.
2. Set up the Cisco Catalyst 3750 and 2970 switches that will handle iSCSI traffic between
servers and the PS Series group members (storage arrays). Be sure to follow these
recommendations, listed in order of significance:
•
It is recommended that you do not use Spanning-Tree (STP) on switch ports that connect
end nodes (iSCSI initiators or storage array network interfaces). If you want to use STP or
RSTP (preferable to STP), enable Cisco’s PortFast option on each switch port that
connects end nodes. PortFast will reduce network interruptions that occur when devices
restart.
Note that the use of Spanning-Tree for a single-cable connection between switches is
encouraged, as is the use of trunking for multiple-cable connections between switches.
2
•
It is recommended that you configure Flow Control on each switch port that handles iSCSI
traffic. PS Series storage arrays will correctly respond to Flow Control if enabled on a
switch. If your server is using a software iSCSI initiator and NIC combination to handle
iSCSI traffic, you must also enable Flow Control on the NICs to obtain the performance
benefit.
•
It is recommended that you disable unicast storm control on each switch that handles iSCSI
traffic. However, the use of broadcast and multicast storm control is encouraged.
•
Configure Jumbo Frames on each switch that handles iSCSI traffic. If your server is using
a software iSCSI initiator and NIC combination to handle iSCSI traffic, you must also
enable Jumbo Frames on the NICs to obtain the performance benefit (or reduce CPU
overhead) and ensure consistent behavior.
Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
Notes: Do not enable Jumbo Frames on switches unless Jumbo Frames is also configured
on the NICs; otherwise, behavior may be inconsistent.
To simplify troubleshooting initial deployments, make sure that NICs, switches,
and PS Series storage arrays are fully operational before enabling Jumbo Frames
on the switches and NICs.
•
Use VLANs to separate iSCSI SAN traffic from other network traffic. PS Series storage
arrays do not support VLAN tagging.
Detailed information about the previous recommendations is provided later in this document.
3. Set up the servers that will access the PS Series group volumes. Servers require an installed
iSCSI initiator to access group volumes, which are seen on the network as iSCSI targets. A
server can use a software iSCSI initiator and network interface card (NIC) combination or an
iSCSI HBA to access group volumes. See the PS Series QuickStart or Group Administration
manual for information about connecting to volumes.
When configuring a software iSCSI initiator and NIC combination on a server, follow these
recommendations:
•
It is recommended that you enable Flow Control on each NIC that handles iSCSI traffic.
Flow Control must also be enabled on the switches that handle iSCSI traffic to obtain the
performance benefit.
•
Enable Jumbo Frames on each NIC that handles iSCSI traffic. Jumbo Frames must also
be enabled on the switches that handle iSCSI traffic to obtain the performance benefit (or
reduce CPU overhead) and ensure consistent behavior.
Notes: Do not enable Jumbo Frames on NICs unless Jumbo Frames is also configured on
the switches that handle iSCSI traffic; otherwise, behavior may be inconsistent.
To simplify troubleshooting initial deployments, make sure that NICs, switches,
and PS Series storage arrays are fully operational before enabling Jumbo Frames
on switches and NICs.
Detailed information about the previous recommendations is provided later in this document.
Understanding Switch and Server Recommendations
The following sections provide more information about the switch and server recommendations for
creating a high-performance and highly-available iSCSI SAN using Cisco Catalyst 3750 and 2970
switches and PS Series storage arrays.
Spanning-Tree
For switch ports that connect end nodes (iSCSI initiators or storage array network interfaces), it is
recommended that you do not use Spanning-Tree (STP). However, if you want to use STP or
RSTP (preferable to STP) for switch ports that connect end nodes, it is recommended that you
Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
3
enable Cisco’s PortFast option on each switch port. PortFast will reduce network interruptions that
occur when devices restart.
Note: The use of Spanning-Tree for a single-cable connection between switches or the use of
trunking for multiple-cable connections between switches is encouraged.
Spanning-Tree Protocol (IEEE 802.1d) is a link management protocol that prevents loops in an
Ethernet network by ensuring that only one active path exists between switches. Upon link up, a
switch performs a 30 to 50 second STP calculation to transition ports into forwarding or blocking
state. During this time, no user data passes through the ports. The result is that links will take
longer to come online. This can cause long failover times when recovering from a network switch
or PS Series storage array control module failover.
Rapid Spanning Tree Protocol (RSTP; IEEE 802.1w) allows a switch port to bypass the SpanningTree listening and learning states and quickly enter the STP forwarding state. In order to achieve
fast convergence on a port, RSTP relies upon two variables: edge ports and link type. Switch ports
connecting end nodes (iSCSI initiators and storage array network interfaces) should be configured
as edge ports to take advantage of RSTP features. However, do not connect other hubs, switches,
concentrators, or bridges to edge ports, because this may cause infinite packet loops.
Some switches have port settings that allow the immediate transition of the port into STP
forwarding state upon link up. If you are using STP or RSTP, these settings should be enabled on
ports that connect end nodes (iSCSI initiators and storage array network interfaces). For example,
Cisco enhanced the original 802.1d STP specification with a proprietary feature called PortFast,
which immediately transitions a port into STP forwarding state upon link up. If you are using STP
or RSTP, switch ports that are connected to end nodes should be configured as edge ports using the
PortFast command. However, do not connect other hubs, switches, concentrators, or bridges to
these ports, because this may cause infinite packet loops.
See your switch documentation for information on Spanning-Tree, in addition to Error! Reference
source not found. in this document.
Flow Control
EqualLogic recommends that you enable Flow Control on the switch ports that handle iSCSI
traffic. In addition, if a server is using a software iSCSI initiator and NIC combination to handle
iSCSI traffic, you must also enable Flow Control on the NICs to obtain the performance benefit.
On many networks, there can be an imbalance in the network traffic between the devices that send
network traffic and the devices that receive the traffic. This is often the case in SAN configurations
in which many servers (initiators) are communicating with storage devices. If senders transmit
data simultaneously, they may exceed the throughput capacity of the receiver. When this occurs,
the receiver may drop packets, forcing senders to retransmit the data after a delay. Although this
will not result in any loss of data, latency will increase because of the retransmissions, and I/O
performance will degrade.
Flow Control allows the receiver to instruct the sender to “throttle back" when the receiver senses
that it is being overwhelmed by packets. The receiver does this by sending "pause frames" to the
sender, which causes the sender to slow packet transmission for a short period of time. This allows
the receiver to process its backlog so it can later resume accepting input. However, the amount of
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Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
delay introduced by this action is dramatically less than the overhead caused by TCP/IP packet
retransmission.
See your switch and NIC documentation for information on enabling Flow Control, in addition to
Enabling the PortFast Option to Configure STP Edge Ports in this document.
Unicast Storm Control
A traffic “storm” occurs when a large outpouring of packets creates excessive network traffic that
degrades network performance. Many switches have traffic storm control features that prevent
ports from being disrupted by broadcast, multicast, or unicast traffic storms on physical interfaces.
These features typically work by discarding network packets when the traffic on an interface
reaches a percentage of the overall load (usually 80 percent, by default).
Because iSCSI traffic is unicast traffic and can typically utilize the entire link, it is recommended
that you disable unicast storm control on switches that handle iSCSI traffic. However, the use of
broadcast and multicast storm control is encouraged.
See your switch documentation for information on disabling unicast storm control, in addition to
Disabling Unicast Storm Control in this document.
Jumbo Frames
EqualLogic recommends that you enable Jumbo Frames on the switch ports that handle iSCSI
traffic. In addition, if a server is using a software iSCSI initiator and NIC combination to handle
iSCSI traffic, you must also enable Jumbo Frames on the NICs to obtain the performance benefit
(or reduce CPU overhead) and ensure consistent behavior.
Ethernet traffic is transported in units called frames. A standard Ethernet frame allows up to 1500
bytes of data to be transferred in a single Ethernet transaction. Jumbo Frames extend Ethernet
frames to 9000 bytes and allow more data to be transferred with each Ethernet transaction.
A PS Series storage array automatically supports standard Ethernet frames and Jumbo Frames up to
9000 bytes (9018 including the TCP header itself). (This is sometimes referred to as the “Alteon
standard.”) PS Series storage arrays also support path MTU, which is the ability to automatically
detect the maximum frame size between TCP/IP end points.
Note:
To take advantage of Jumbo Frames, all devices in the network path between servers and
the PS Series group⎯including the switches and the NICs used to access volumes⎯must
have Jumbo Frames enabled.
Switches configured for Jumbo Frames will support both standard Ethernet frames and
Jumbo Frames. However, if a NIC is configured for Jumbo Frames, but the switch is not,
you may experience inconsistent behavior. The switch will function properly if the frames
are small, but once the NIC attempts to send frames larger than 1500 bytes, the switch will
not be able to handle the frames and will drop them. Also, if some switches are configured
for Jumbo Frames, but others are not, you may experience inconsistent behavior if routing
changes occur after the connection has been established.
Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
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Many low and mid-range network switches do not support Jumbo Frames. On switches that do
support them, the feature is usually disabled by default, so you need to manually enable it.
Usually, VLANs must be enabled in order to enable Jumbo Frames on switches. See the switch
documentation for details, in addition to Configuring Jumbo Frames in this document.
VLANs
EqualLogic recommends that you use virtual LANs (VLANs) to enable network switches to
separate iSCSI SAN traffic from other network traffic. VLANs provide benefits similar to those of
separate network switches, but with fewer physical switches and less management overhead.
Because VLANs use logical rather than physical connections, they are flexible to operate.
Note: PS Series storage arrays do not support VLAN tagging.
Typically, VLANs are separate subnets in TCP/IP networks, so connectivity between VLANs
usually requires L3 routing, which is a capability of the Cisco Catalyst 3750 and 2970 switches.
VLANs also support different network settings, including Jumbo Frames. See Jumbo Frames for
more information.
Separating iSCSI SAN traffic from LAN traffic also allows you to enable switch-based security
enhancements, including port blocking, address filtering, etc.
Catalyst 3750 and 2970 Switch Configuration
The following sections provide information about configuring Cisco Catalyst 3750 and 2970
switches. For additional information, see:
•
Cisco Catalyst 3750 switch:
Website: http://www.cisco.com/en/US/products/hw/switches/ps5023/index.html
Documentation: http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3750/index.htm
•
Cisco Catalyst 2970 switch:
Website: http://www.cisco.com/en/US/products/hw/switches/ps5206/index.html
Documentation: http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2970/index.htm
Also, see the following manuals:
•
Cisco Catalyst 3750 Switch Software Configuration Guide:
http://www.cisco.com/application/pdf/en/us/guest/products/ps5023/c2001/ccmigration_09186a
008017ed8d.pdf
•
Cisco Catalyst 2970 Switch Software Configuration Guide:
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2970/12119ea1/2970scg/2970scg.pdf
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Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
Cisco Switch Interfaces
For Cisco Catalyst 3750 and 2970 switches, an interface name is composed of three parts that are
formatted as follows:
slot_number/interface_module_number/port_number
The variables are as follows:
•
slot_number - The switch slot in which the interface module is installed. Module slots are
numbered 0 to 12, from top to bottom. In the case of the Cisco 3750 switch, the first switch in
a stack is slot number 1; then, the slot numbers increase by one for each switch added to the
stack. In the case of the Cisco 2970 switch, the slot number is always 1. If not specified in a
command, the default value will be the slot or switch to which you are currently connected.
•
interface_module_number - The number of the interface module for this port. When the
module consists of a single card or, in the case of the Cisco 3750 and 2970, this number is
always 0.
•
port_number - The port number on the interface module or, in the case of the Cisco 3750 and
2970, the port number on the switch. Also, keep in mind that, for some commands, you can
assign several ports at once by using wildcards, such as 1/0/1-12 for the first twelve ports on
module 0, switch 1.
Enabling the PortFast Option to Configure STP Edge Ports
To configure STP edge ports on Cisco Catalyst 3750 and 2970 switches, you must enable the
PortFast option. PortFast minimizes the time that ports must wait for Spanning-Tree to converge
and should only be used on ports connected to end nodes (end stations), including iSCSI initiators
and storage array network interfaces.
Caution: Connecting hubs, concentrators, switches, or bridges to a port that has PortFast enabled
can cause temporary spanning-tree loops. You should not enable PortFast on these
ports.
The following example shows how to enable PortFast on Gigabit Ethernet interface 0/1 on
switch 1:
Switch> enable
Switch# config t
Switch(config)# int gigabit 1/0/1
Switch(config-if)# spanning-tree portfast
Switch(config-if)# exit
Switch(config)# exit
Switch# copy running-config startup-config
To view or confirm Port Fast status on a port, use the following command.
Switch# show spanning-tree interface gigabitethernet0/1
Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
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Note: You can use the spanning-tree portfast default global configuration command to
globally enable the PortFast feature on all nontrunking ports.
This example shows how to globally enable PortFast by default on all access ports:
Switch# config t
Switch(config)# spanning-tree portfast default
Switch(config)# end
Switch# copy running-config startup-config
See the Cisco Catalyst 3750 Switch Software Configuration Guide or the Cisco Catalyst 2970
Switch Software Configuration Guide for information on configuring Spanning-Tree Protocol.
For additional information on understanding and configuring Spanning-Tree Protocol on Catalyst
switches, see:
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_configuration_example09186a008009
467c.shtml
Configuring Flow Control
This section describes how to configure Flow Control on Cisco Catalyst 3750 and 2970switches.
You must enable Flow Control on each switch port that handles iSCSI traffic.
Note: Cisco Catalyst 3750 and 2970 switch ports are capable of receiving, but not sending, pause
frames.
The following commands shows how to configure Gigabit Ethernet interface 0/1 on switch 1 to
auto-negotiate the correct Flow Control setting with the device to which it is connected:
Switch> enable
Switch# configure terminal
Switch(config)# interface gigabitethernet1/0/1
Switch(config-if)# flowcontrol receive desired
Switch(config-if)# exit
Switch(config)# exit
Switch# copy running-config startup-config
To view or confirm Flow Control status on a port, use the following command:
Switch# show flowcontrol interface gigabitethernet1/0/1
See the Cisco Catalyst 3750 Switch Software Configuration Guide or the Cisco Catalyst 2970
Switch Software Configuration Guide for detailed information on configuring Flow Control.
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Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
Disabling Unicast Storm Control
This section describes how to disable unicast storm control on Cisco Catalyst 3750 and 2970
switches.
The following example shows how to disable unicast storm control on Gigabit Ethernet interface
0/15 on switch 1 and verify the configuration:
Switch> enable
Switch# configure terminal
Switch(config)# interface gigabitethernet1/0/15
Switch(config-if)# no storm-control unicast level
Switch(config-if)# exit
Switch(config)# exit
Switch# copy running-config startup-config
To view or confirm storm control status on a port, use the following command.
Switch# show storm-control gigabitethernet1/0/15 unicast
Interface Filter State
Level
Current
--------- ------------- ------ ------Gi2/0/15
inactive
100.00% N/A
For more information on configuring port-based traffic control on Catalyst switches, see:
http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_guide_chapter
09186a008021272b.html
Configuring Jumbo Frames
On Cisco Catalyst 3750 and 2970 switches, you cannot set the MTU size for an individual
interface. Instead, you must set it for all Gigabit Ethernet interfaces on the switch, or for all
interfaces in a VLAN. When you change the MTU size, you must reset the switch before the new
configuration takes effect. If you enter a value that is outside the allowed range for the specific
type of interface, the value is not accepted.
Use the following commands to configure Jumbo Frames, which sets the maximum packet size to
9000 bytes, on Cisco Catalyst 3750 and 2970 switches:
Switch> enable
Switch# config t
Switch(config)# system mtu jumbo 9000
Switch(config)# exit
Switch# copy running-config startup-config
Switch# reload
The following example shows the output when you try to set Gigabit Ethernet interfaces to an outof-range number:
Switch(config)# system mtu jumbo 25000
^
% Invalid input detected at '^' marker.
Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
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Once the switch reloads, you can verify your settings by entering the show system mtu
privileged EXEC command. For example:
Switch> enable
Switch# configure t
Switch(config)# show system mtu
Switch(config)# exit
The commands shown next are used to enable an individual VLAN to use Jumbo Frames. Note
that you cannot enable Jumbo Frames on VLAN 1 on the 3750 or 2970 switch, so you must start
with VLAN 2.
Switch# vlan database
Switch(vlan)# vlan 2 mtu 9000
Switch(vlan)# exit
The following commands configure Gigabit Ethernet interface 0/7 on switch 1 into VLAN 2:
Switch# config t
Switch(config)# int gigabitethernet 1/0/7
Switch(config-if)# switchport access vlan 2
Switch(config-if)# exit
Switch(config)# exit
Switch# copy running-config startup-config
To view or confirm MTU size on a port, use the following command.
Switch# show interface gi 1/0/7
For more information on configuring Jumbo Frames or Giant Frames on Catalyst switches, see:
http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a
008010edab.shtml
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Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
Documentation and Customer Support
Visit the EqualLogic Customer Support website, where you can download the latest documentation
and firmware. You can also view FAQs, the Knowledge Base, and Tech Reports and submit a
service request.
EqualLogic PS Series storage array documentation includes the following:
•
Release Notes. Provides the latest information about PS Series storage arrays and groups.
•
QuickStart. Describes how to set up the hardware and start using a PS Series storage array.
•
Group Administration. Describes how to use the Group Manager GUI to manage a PS Series
group. This manual provides comprehensive information about product concepts and
procedures.
•
CLI Reference. Describes how to use the Group Manager command line interface to manage a
group and individual arrays.
•
Hardware Maintenance. Provides information on maintaining the PS Series storage array
hardware.
To access the Customer Support website, from the EqualLogic website (www.equallogic.com),
click Support and log in to a support account. If you do not have an account, create one by
clicking the link under the login prompt.
To contact customer support, send e-mail to supportnp@equallogic.com. If the issue
is urgent, call 1-877-887-7337 to speak with a member of the customer support team.
Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group
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