How To SAP HANA System Replication

SAP How-to Guide
Business Analytics
SAP HANA™ Appliance
How To Perform System Replication for SAP HANA
Applicable Releases:
SAP HANA 2.0 SPS00
Version 5.0
January 2017
For additional information contact:
mechthild.bore-wuesthof@sap.com
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Document History
Document
Version
Description
1.0
First official release of this guide
1.1
Small updates and language edit
1.2
Some descriptions were corrected
2.0
Update with HANA 1.0 SPS07 and SPS08 features
2.3
Minor corrections
2.4
Secondary site usage for QA/DEV – small update
2.6
Reference to docu on e-mail notification for alerts
3.0
Update with HANA 1.0 SPS09 features
3.1
Minor corrections
3.2
Fixed return codes of systemReplicationStatus.py
3.3
Updated network settings & sr_state output
3.4
Corrected system replication hostname resolution
3.5
Update with HANA 1.0 SPS10 features
4.0
Update with HANA 1.0 SPS11 features & minor corrections
4.1
Update with HANA 1.0 SPS12 features & minor additions
4.2
Minor corrections
4.3
Minor corrections
5.0
HANA 2.0 – including Active/Active (read enabled)
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Table of Contents
1.
Business Scenario ........................................................................................ 1
2.
Before you start............................................................................................ 1
3.
Background Information ............................................................................. 2
3.1 High Availability....................................................................................... 2
3.2 System Replication ................................................................................. 3
3.2.1 Replication modes ....................................................................... 4
3.2.2 Operation modes ......................................................................... 4
3.2.3 Data transferred to the secondary ............................................. 5
3.3 Takeover .................................................................................................. 7
4.
Planning........................................................................................................7
4.1 Prerequisites ........................................................................................... 7
4.2 Distance between data centers ............................................................. 9
4.3 Use secondary site for DEV/QA system ............................................... 9
4.4 License Validity ..................................................................................... 10
5.
Configuration steps .................................................................................... 10
5.1 Configure system replication ................................................................ 11
5.1.1 Using SAP HANA cockpit 2.0 ..................................................... 11
5.1.2 Using SAP HANA studio ............................................................ 18
5.1.3 Using command line tool hdbnsutil ...................................... 21
5.1.4 Creating a tenant DB in a running system replication ............. 22
5.2 Disable system replication ................................................................... 22
5.2.1 Using SAP HANA cockpit 2.0 .................................................... 22
5.2.2 Using SAP HANA studio ............................................................ 24
5.2.3 Using command line tool hdbnsutil ...................................... 25
5.3 Setting up Multitier System Replication .............................................26
5.3.1 Using SAP HANA cockpit 2.0 .................................................... 27
5.3.2 Using SAP HANA studio ........................................................... 30
5.3.3 Using command line tool hdbnsutil ...................................... 32
5.4 Enabling full sync replication ............................................................... 32
5.5 Change replication mode ..................................................................... 33
6.
Takeover.................................................................................................... 33
6.1 Perform Takeover ................................................................................. 33
6.1.1 Using SAP HANA cockpit 2.0 .................................................... 33
6.1.2 Using SAP HANA studio ............................................................ 35
6.1.3 Using command line tool hdbnsutil ......................................36
6.2 Client connection recovery .................................................................. 37
7.
Resync optimization .................................................................................. 37
7.1 Data Retention ...................................................................................... 37
7.2 Log Retention ........................................................................................38
7.2.1 Log Retention for Secondary Disconnect (on primary) ..........38
7.2.2 Log Retention for Failback (on secondary) ..............................39
7.2.3 Log Retention Parameters ....................................................... 40
7.2.4 Maximum Retention Time Estimation ...................................... 41
8.
Active/Active (read enabled) secondary ................................................... 41
8.1 Active/Active read-only specifics ........................................................ 42
8.2 Check Active/Active configuration ..................................................... 42
8.2.1 Using the command line ............................................................ 42
8.2.2 Using SAP HANA cockpit 2.0 ....................................................43
8.2.3 Using HANA studio ....................................................................44
8.3 Connection types ..................................................................................44
8.3.1 Explicit read-only connection to secondary .............................44
8.3.2 Statement routing from primary to secondary........................ 45
9.
Testing ...................................................................................................... 46
10.
Operation / Maintenance .......................................................................... 47
10.1.1 Alerts ........................................................................................... 47
10.2 Verification ............................................................................................49
10.2.1 Using SAP HANA cockpit 2.0 ....................................................49
10.2.2 Using SAP HANA studio ............................................................ 54
10.2.3 Check via SQL query .................................................................. 55
10.2.4 Using command line tool hdbnsutil ...................................... 56
10.3 System Replication status checks....................................................... 57
10.3.1 Using landscapeHostConfiguration.py .......................... 58
10.3.2 Using systemReplicationStatus.py................................. 59
10.3.3 Using console ............................................................................ 60
10.3.4 Using predefined SQL statement..............................................62
10.4 Monitoring and replicating ini parameter changes .......................... 65
10.5 Monitoring the secondary site ............................................................. 67
10.6 System replication connection ............................................................70
10.6.1 Secure configuration of the connection ...................................70
10.6.2 Allowed senders for the connection ......................................... 73
10.6.3 Encryption of the connection .................................................... 73
10.6.4 Data and Log compression for transfer ................................... 74
10.6.5 Monitoring the connection ........................................................ 74
10.7 Upgrade and Maintenance ................................................................... 75
10.7.1 “Normal” Upgrade ..................................................................... 76
10.7.2 Near Zero Downtime Upgrade .................................................. 76
10.7.3 Hardware Exchange ................................................................... 78
11.
Further documentation ............................................................................. 78
11.1 Whitepapers and HowTo guides .......................................................... 78
11.2 Official Guides ....................................................................................... 79
How To System Replication for SAP HANA
1.
Business Scenario
Business Continuity requires that the operation of business critical systems
remain highly available at all time, even in the presence of failures. High availability
and disaster recovery are the building blocks to support this.
Among other features, SAP HANA provides the possibility to replicate your SAP
HANA system within the same or over two data centers. This paper briefly
describes SAP HANA System Replication in a step-by-step manner to support
High Availability and Disaster Recovery and references the needed guides for
details.
2.
Before you start
It is recommended to have studied the following documents, which are frequently
referred to in this document:





SAP HANA High Availability Whitepaper:
http://scn.sap.com/docs/DOC-65585
SAP HANA Administration Guide:
http://help.sap.com/hana/SAP_HANA_Administration_Guide_en.pdf
SAP HANA Master Guide:
http://help.sap.com/hana/SAP_HANA_Master_Guide_en.pdf
SAP HANA Server Installation Guide:
http://help.sap.com/hana/SAP_HANA_Server_Installation_Guide_en.pdf
SAP HANA Security Guide:
http://help.sap.com/hana/SAP_HANA_Security_Guide_en.pdf
The first document will give a broad overview and basic knowledge to understand
what this paper discusses.
Additionally there is a set of SAP HANA Academy videos available, which are worth
watching:

SAP HANA Academy on system replication:
http://scn.sap.com/community/hana-in-memory/blog/2015/05/19/saphana-system-replication

SAP HANA Academy on “What’s New with HANA 2.0 SPS00”:
https://blogs.sap.com/2016/12/21/sap-hana-2.0-sps-00-whats-new-highavailability-by-the-sap-hana-academy/
You should also be aware of these SAP notes containing valuable information on 
SAP HANA system replication:
 SAP Note 2369981 - Required configuration steps for authentication with
HANA System Replication
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How To System Replication for SAP HANA






SAP Note 1999880 - FAQ: SAP HANA System Replication
SAP Note 2165547 - FAQ: SAP HANA Database Backup & Recovery in an
SAP HANA System Replication Landscape
SAP Note 1945676 - Correct usage of hdbnsutil -sr_unregister
SAP Note 1984882 – Using HANA system replication for Hardware
Exchange with Minimum Downtime
SAP Note 2063657 - HANA System Replication takeover decision guideline
SAP Note 1913302 - Connectivity suspend of Appserver during takeover.
The following blogs also discuss the topic; please feel free to comment:

HANA System Replication - Takeover process:
http://scn.sap.com/docs/DOC-52345

HANA System Replication – Backup:
http://scn.sap.com/docs/DOC-53608

HANA System Replication – Switching back and forth:
http://scn.sap.com/community/hana-in-memory/blog/2013/12/16/saphana-system-replication--using-hdbnsutil-sr
For information about SAP HANA in general, see:
http://help.sap.com/hana_appliance
3.
Background Information
3.1
High Availability
SAP HANA offers different kinds of high availability mechanisms, supporting a
broad range of recovery scenarios from various faults.
There are three basic scenarios:

Host Auto-Failover: One (or more) standby nodes are added to an SAP
HANA system and configured to work in standby mode. (SAP HANA scaleout)1.

Storage Replication: The storage itself replicates all data to another location

(this solution is provided by hardware partners). Disks are mirrored without
a control process from the SAP HANA system.
System Replication: SAP HANA replicates all data to a secondary SAP
HANA system (standard SAP HANA feature). Data is constantly pre-loaded
on the secondary system to minimize the recovery time objective (RTO).
1
For technical details of this solution, please refer to the Host Auto-Failover technical document:
http://scn.sap.com/docs/DOC-62494
2
How To System Replication for SAP HANA
This paper focuses on supporting decision making on SAP HANA system
replication including setting up, testing and maintaining such a system. Of course,
a comprehensive high availability solution offers more design choices and requires
the discussion of more details than can be covered in a short paper; thus,
additional consultation may be required.
3.2
System Replication
SAP HANA system replication ships all data to a secondary system located at
another site:
Overview of System Replication with single node HANA databases
Once SAP HANA system replication is enabled, each server process on the
secondary system establishes a connection with its primary counterpart and
requests a snapshot of the data. Now all logged changes in the primary system are
replicated continuously. Each persisted redo log in the primary system is sent to
the secondary system. A transaction in the primary system is not committed
before the redo logs are replicated.
SAP HANA Multitenant Database Containers (introduced with HANA 1.0 SPS09)
can also run in an SAP HANA system replication configuration. The system as a
whole is replicated2, i. e. the System DB and all tenant DBs. Just like in the single
container HANA database each service with a persistency (i. e. data and log
volume) of the primary site replicates to its counterpart on the secondary site.
2
Note that SAP HANA system replication on tenant database level is not supported.
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How To System Replication for SAP HANA
While the system replication is running, the secondary system, which is configured
identically to the primary system, will be on standby until a takeover takes place.
As of HANA 2.0 SPS00 the secondary system can also be used for read access, if
configured as Active/Active (read enabled) system.
3.2.1 Replication modes
Depending on customer requirements, SAP HANA offers different modes for
replication of the redo log:



Synchronous: Secondary system sends acknowledgement back to primary
as soon as data are received and persisted to the log volumes on disk.
Synchronous in-memory: Secondary system sends acknowledgement back
to primary as soon as data is received in memory; the disk I/O speed on the
secondary does not influence the primary’s performance.
Asynchronous: As per design of asynchronous replication, the primary does
not wait until the secondary sends an acknowledgement.
Additionally (as of HANA 1.0 SPS08) the synchronous replication mode (SYNC)
can run with “full sync” enabled. In full sync operation, transaction processing on
the primary site blocks, when the secondary is currently not connected and newly
created redo log buffers cannot be shipped to the secondary site. This behavior
ensures that no transaction can be committed locally without shipping the redo log
buffers to the secondary site.
3.2.2 Operation modes
Since HANA 2.0 SPS00 SAP HANA system replication can be run in three different
operation modes:



delta_datashipping: In addition to the continuous redo log shipping taking
place the secondary system requests a delta data shipping from time to
time (per default every 10 minutes). During takeover the redo log needs to
be replayed up to the last arrived delta data shipment. (This is the
“classical” operation mode of SAP HANA system replication.)
logreplay: In this operation mode (since HANA 1.0 SPS11) pure redo log
shipping is done after the system replication was initially set up with one full
data shipping. The redo log is replayed on the secondary immediately after
arrival making this step superfluous during a takeover, which shortens the
RTO by factors. Additionally the amount of data which needs to be
transferred to the secondary site is reduced dramatically, because no delta
data shipping is required anymore.
logreplay_readaccess: Regarding the continuous log shipping, the redo log
replay on the secondary site as well as the required initial full data shipping
and the takeover, this operation mode (since HANA 2.0 SPS00) behaves
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How To System Replication for SAP HANA
just like the “logreplay” operation mode. The difference is that here the
secondary system is read enabled, i. e. SQL SELECT queries are possible3.
By establishing a direct connection to the secondary database or by
providing a SELECT statement from the primary with a HINT, read access is
possible on the Active/Active (read enabled) secondary system.
Using the operation mode logreplay makes your secondary site in the SAP
HANA system replication a HotStandby system; using operation mode
logreplay_readaccess allows for read-only access on the read enabled
secondary system making an Active/Active (read enabled) system out of your
system replication landscape.
Note
In a multitier system replication only one operation mode is allowed for the
whole landscape, with one exception: If operation mode
logreplay_readaccess is configured between primary (tier-1) and the
tier-2 secondary, then operation mode logreplay is allowed between tier-2
and tier-3 secondary.
3.2.3 Data transferred to the secondary
The HANA database sends two resp. three types of data “packages” over the
network to the secondary side (depending on the configured operation mode),
when system replication is configured:

Full data shipping: A full set of the data created as HANA in-place snapshot
on the disk of the primary is initially sent when system replication is set up.4

Delta data shipping: Only in delta_datashipping operation mode the
increment of the data (i.e. every data that has changed since the last full or
the last delta data shipping), is transported from time to time (default every
10 minutes) from the data area of the primary to the data area of the
secondary.

Redo Log shipping: Every committing write transaction on the primary
generates redo log buffers that are continuously sent to the secondary site.
The following picture visualizes this traffic on the transportation channel between
primary and secondary for the delta_datashipping operation mode.
3 For read access details on the secondary system please refer to 2391079 - Access restrictions in Active/Active system
setup.
4 If the connection between primary and secondary is weak and it would take very long to get this initial full data shipping
through the network channel, as of HANA 1.0 SPS12 the secondary system can be initialized with a consistent storage
snapshot. Please see the SAP HANA Administration guide – section: Initialize the Secondary with Storage Copy from
Primary
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How To System Replication for SAP HANA
Operation mode delta_datashipping:
Initial full data shipping, frequent delta data shipping
and continuous redo log shipped to secondary
In logreplay or logreplay_readaccess operation mode the delta data
shipping is not required.
Operation mode logreplay or logreplay_readaccess
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How To System Replication for SAP HANA
Initial full data shipping and continuous redo log shipping to secondary
3.3
Takeover
The takeover process is the name for the task of switching your active system
from the current primary system onto the secondary system5. Once the takeover
command runs, the former secondary system becomes the new “primary” system
– more correctly, it becomes your new actively running system.
The takeover automatically performs some tasks before the system is fully
available:




4.
Until HANA 1.0 SPS08 the row store tables were loaded into memory during
takeover; since HANA 1.0 SPS09 the row store is kept in shared memory
and thus is “pre-loaded”.
Until HANA 1.0 SPS09 the row store indexes were rebuilt during takeover;
with HANA 1.0 SPS10 rebuilding the secondary indexes during reactivation
of the row store is done in a decoupled way, so it does not influence the
takeover performance.
Until HANA 1.0 SPS10 the redo log buffers shipped to the secondary site
since the last delta data transport could first be replayed during takeover;
with the two logreplay* operation modes (logreply since HANA 1.0
SPS11 and logreplay_readaccess since HANA 2.0 SPS00) the log is
continuously replayed on the secondary site, increasing the takeover
performance.
If preload is used, the main parts of the column tables are already loaded
into memory, as they were loaded in the primary. The first access to a table
that was previously used in the primary loads the delta part only. The delta
part is typically much smaller than the main part and can be loaded within
seconds in most cases.
Planning
Let us discuss some facts, which need to be considered or decided during the
planning phase.
4.1
Prerequisites
Before you start setting up SAP HANA system replication, your HANA databases
need to fulfill the following prerequisites:
5
Note that a takeover does not include stopping the previous primary, if it is still running after takeover, if you did not take
measures to stop it!
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How To System Replication for SAP HANA
 The primary and secondary systems are both installed and configured. You
have verified that both are independently up and running.
 In HANA 2.0 the System PKI SSFS key and data files were copied from the
primary to the secondary site according to this SAP Note 2369981. The files
can be found here:
$DIR_INSTANCE/../global/security/rsecssfs/data/SSFS_<SID>.DAT
$DIR_INSTANCE/../global/security/rsecssfs/key/SSFS_<SID>.KEY
 The number of nodes in the secondary system has to be equal to the number
of active nodes in the primary system. (As of HANA 1.0 SPS06 the secondary
system does not need to have standby nodes.)
 All configuration steps have to be executed on the master name server node;
for SAP HANA Multitenant Database Containers this means on the System
DB (and not on the tenant DBs).
 The SAP HANA software version of the secondary has to be equal to or newer
than the one on the primary; however, if you want to make use of a read
enabled secondary system in an Active/Active (read enabled) configuration,
the SAP HANA software versions have to be identical.
 The secondary system must have the same SAP system ID, <SID>, and
instance number as the primary system. The primary replicates all relevant
license information to the secondary.
 System replication between two systems on the same host is not supported.
 Changes to the ini file configuration parameters made on one system
should be duplicated on the other system.
As of HANA 1.0 SPS06 the configuration parameter checker reports
differences between primary and secondary parameter settings (generating
alerts in the SAP HANA studio). As of HANA 1.0 SPS12 INI parameters can
be replicated to the secondary system.
 The required ports must be available. The same <instance number> is
used for primary and secondary systems. The <instance number>+1 must
be free on both systems, because this port range is used for system
replication communication.6
 An initial data backup or snapshot must be performed on the primary before
the system replication can be activated. In SAP HANA Multitenant Database
Containers all databases must have been backed up, i. e. the system DB as
well as all tenant DBs7.
6
For additional port specific information in Multitenant Database Containers running in System Replication please refer to
http://help.sap.com/hana/SAP_HANA_Administration_Guide_en.pdf - section:SAP HANA System Replication with
Multitenant Database Containers
In an already running SAP HANA system replication for a Multitenant Database Container HANA, every newly created
tenant DB has to be backed up for the replication to start.
7
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How To System Replication for SAP HANA
4.2
Distance between data centers
System replication offers synchronous and asynchronous replication modes to
accommodate network latency.
If the distance between your sites is less than 100 km you can use a synchronous
replication mode: SYNC or SYNCMEM.
For all data centers that are more than 100 km apart, the asynchronous replication
mode ASYNC is recommended.
Note
Depending on latency, data volume, volume of changed data records, this
could lead to loss of changes because of missing redo logs. Please also
consider monitoring requirements for asynchronous mode.
4.3
Use secondary site for DEV/QA system
For system replication landscapes not running in an Active/Active (read enabled)
configuration (with operation mode “logreplay_readaccess”) it is possible to
make use of the secondary site for running DEV/QA systems while the primary
system is in production. However, for Active/Active configured systems, this is
currently not supported.
The following prerequisites must be taken into account:



Additional independent disk volume is needed for DEV/QA systems; since
the secondary requires the same I/O capacity as the primary the additional
systems must not have a negative impact on the secondary’s I/O – thus it is
recommended to have a separated storage infrastructure for each system.
The SIDs and instance numbers have to be different for DEV/QA. The
<instance number>+1 of the productive system must not be used but
must be free on both sites, because this port range is used for system
replication communication.
Preload of tables must be switched off on the secondary system:
global.ini/[system_replication]-> preload_column_tables=false



The takeover process will take longer as no data is preloaded to memory on
the secondary site (could still meet SLAs for disaster recovery)
DEV/QA systems need to be shut down in case of a takeover.
Additionally, the global allocation limit on the secondary system must be set
in a way that the available memory covers the memory needed by the
secondary system as well as the DEV/QA systems:
global.ini/[memorymanager]-> global_allocation_limit
As of HANA 1.0 SPS11 the configured operation mode influences the
memory size required on the secondary:
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How To System Replication for SAP HANA
operation mode
memory needed on secondary
delta_datashipping
minimum 64 GB
or
row store size8 + 20 GB (if this sum is
higher)9
logreplay
size of loaded column tables (in-memory)10
+ row store size4 + 50 GB
logreplay_readaccess No other systems allowed on read enabled
secondary
If the row store size grows during operation of the primary, it might become
necessary to increase the global_allocation_limit on the secondary
site. As of HANA 1.0 SPS07 it is possible to change the global.ini on the
secondary accordingly and then activate the change with “hdbnsutil –
reconfig” (because no SQL is possible in this state).
4.4
License Validity
The primary system automatically replicates relevant license information to the
secondary. No additional license needs to be installed, since the primary and
secondary have the same SID.
Further information on licensing in SAP HANA system replication can be found in
SAP note 2211663.
5.
Configuration steps
This section describes the following steps:




Perform an initial data backup or a storage snapshot using native HANA
options. An initial data backup or snapshot is mandatory but an up-to-date
backup is highly recommended anyway
Enable the primary system for system replication
Establish a connection between secondary and primary system
Initiate a full data replication by configuring system replication on the
secondary and starting it – thereafter incremental data replication (only in
8
The row store size can be determined with this SQL statement:
select host, round(sum(page_size*USED_BLOCK_COUNT)/1024/1024/1024,2) as "RowStore Size GB"
from m_data_volume_page_statistics where page_sizeclass = '16k-RowStore' group by host;
9
If this limit is not set, the HANA database on the secondary site uses as much memory as it can get and possibly takes it
away from the DEV/QA systems, which could run into out-of-memory.
10 The size of loaded column tables (in-memory) can be found with this SQL statement:
select round(sum(memory_size_in_total)/1024/1024/1024) size_GB from m_cs_tables;
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How To System Replication for SAP HANA
delta_datashipping operation mode) and continuous redo log
replication (in both logreplay operation modes) starts automatically
 Disable system replication on secondary system
 Disable system replication on primary system
 Monitor status of system replication to ensure that both systems are active
and in sync
System replication can be set up in three ways: on the console via command line,
using the SAP HANA cockpit 2.0 or the SAP HANA studio. The primary system
stays online during this procedure.
SAP HANA cockpit 2.0 and SAP HANA studio provide an easy way to set up and
maintain system replication, whereas during run time the command line will
probably be used, because it can be a part of a script, which executes further steps
beyond system replication.
5.1
Configure system replication
To configure system replication the primary system must have been backed up (at
least) once. Thus in the following sections the steps to create a full data backup or
database snapshot are described as well although they do not have to be executed,
if the system was backed up before in its lifetime (also see the section Backup and
Recovery in the SAP HANA Administration Guide).
Note
To configure SAP HANA system replication for SAP HANA Multitenant
Database Containers all configuration steps have to be done on the
SystemDB.
5.1.1 Using SAP HANA cockpit 2.0
Use the SAP HANA cockpit 2.0 to set up system replication between two
identically configured systems. You have registered these systems in the HANA
cockpit 2.0 and they are accessible there:
To create a full data backup on the system overview page of your primary system
click on “Manage database backups”:
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How To System Replication for SAP HANA
Click on “Create Backup”:
Create a complete data backup and chose a backup location – click “Back Up”:
The backup progress running per service is shown:
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How To System Replication for SAP HANA
The backup success is then reported with the following screen – showing a data
backup for each service:
Go back to the previous screen (by clicking on “<”) where you get a view of the
data backups contained in the backup catalog:
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How To System Replication for SAP HANA
Note
In SAP HANA Multitenant Database Containers, the data backups must be
created for the System DB as well as for all tenant DBs. However, the SAP
HANA system replication setup steps described in the following sections
have to be executed on the System DB only.
To configure system replication proceed as follows:
Back on the system overview page of your primary system you will see “System
replication is not yet enabled for this system” on your freshly installed system.
Click on the System Replication tile to configure this primary site:
In the System Replication Overview you see “Not Configured”. Click on “Configure
System Replication” to enable this system to run as primary:
Enter a site name for the primary site and click on “Configure”:
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How To System Replication for SAP HANA
The overview now shows that this HANA system is enabled to function as primary
in a SAP HANA system replication:
To register the second HANA system to function as secondary site in the system
replication landscape, go to the system overview page of the to-be-secondary
system. Click on the “Overall Database Status” tile, because the database needs to
be offline for registering it as a secondary system:
Stop the to-be-secondary system by clicking on “Stop System”:
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How To System Replication for SAP HANA
Back on the secondary’s system overview the corresponding tile now shows:
Click on the System Replication tile to enter the configuration dialogue:
In the system replication overview click “Register Secondary System”:
Enter the secondary’s site name, the requested replication mode, the requested
operation mode and the primary’s master host name and click “Configure”:
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How To System Replication for SAP HANA
Once the secondary system is started, the replication process will start
automatically.
After configuration click on “<” and you will get the current system replication
status from the secondary’s point of view:
On the system HANA cockpit 2.0 overview pages for the primary system and the
secondary system you will see these tiles – in this case telling you that everything
worked well and that the replication is active and in sync for all services:
Primary:
Secondary:
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How To System Replication for SAP HANA
5.1.2 Using SAP HANA studio
Use the SAP HANA studio to set up system replication between two identically
configured systems:
Create a data backup of the primary system11. Right mouse-click on dedicated
primary  Backup and Recovery Back Up System:
Note
Alternatively you could create a storage snapshot. Right mouse-click on
dedicated primary  Backup and Recovery  Manage Storage Snapshot:
11
In SAP HANA Multitenant Database Containers, the System DB as well as all tenant DBs have to be backed up.
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How To System Replication for SAP HANA
Prepare:
Confirm:
To configure system replication proceed as follows:
Right mouse-click on Primary System  Configuration and Monitoring 
Configure System Replication12 … . Check the radio button to enable system
replication:
12 Only the actions that are possible in the current system state will be offered to you. In this case only the “enable” is
possible.
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How To System Replication for SAP HANA
Give the primary a logical site name, for example SITEA:
Stop the secondary system with right mouse-click on Secondary System 
Configuration and Monitoring  Stop System
Caution
If you are running with HANA 2.0 you will need to copy the systemPKI SSFS
key and data file from the primary to the secondary before registering the
secondary site. The corresponding files can be found on the primary:
$DIR_INSTANCE/../global/security/rsecssfs/data/SSFS_<SID>.DAT
$DIR_INSTANCE/../global/security/rsecssfs/key/SSFS_<SID>.KEY
Register13 the secondary: Right mouse-click on Secondary System 
Configuration and Monitoring  Configure System Replication … Check radio
button “Register secondary system”:
Type a logical name (= site name) for the secondary, choose a replication mode,
an operation mode14, and enter the primary site’s host name:
If problems occur indicating an error like “unable to contact primary site” and “bad certificate”, please follow the
procedure described in the SAP HANA Security guide – section: Secure Internal Communication between Sites in System
Replication Scenarios.
14 Caution: Since SAP HANA studio will not be supported anymore and will be replaced by SAP HANA cockpit, the operation mode
13
“logreplay_readaccess” to configure Active/Active (read enabled) system replication is not available here.
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How To System Replication for SAP HANA
Once the secondary system is automatically started, the replication process will
also start automatically.
5.1.3 Using command line tool hdbnsutil
Alternatively use the command line tool hdbnsutil as <sid>adm on OS level.
Create a data backup of the primary system:
hdbsql BACKUP DATA USING FILE ('<path><prefix>')
Note
In SAP HANA Multitenant Database Containers all databases must be
backed up using the “hdbsql” tool via the database name option:


for the system DB “-d SystemDB” resp.
for the tenant DBs “-d <tenantDBName>”.
Enable the primary system and give the primary a logical name, for example
SITEA:
hdbnsutil -sr_enable --name=SITEA
Caution
If you are running with HANA 2.0 you will need to copy the systemPKI SSFS
key and data file from the primary to the secondary before registering the
secondary site – if you not already have done that. The corresponding files
can be found on the primary:
$DIR_INSTANCE/../global/security/rsecssfs/data/SSFS_<SID>.DAT
$DIR_INSTANCE/../global/security/rsecssfs/key/SSFS_<SID>.KEY
Stop the secondary system:
sapcontrol –nr <instance_number> -function StopSystem HDB
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How To System Replication for SAP HANA
Register the secondary system, provide a logical name (for example SITEB), and
choose a replication mode and the operation mode:
hdbnsutil -sr_register
--remoteHost=<primary hostname>
--remoteInstance=<instance number>
--replicationMode=<sync|syncmem|async>
--operationMode=<delta_datashipping|logreplay|logreplay_readaccess>
--name=SITEB
Start the secondary system to start replication:
sapcontrol –nr <instance_number> -function StartSystem HDB
Once the secondary system is started, the replication process will start
automatically.
5.1.4 Creating a tenant DB in a running system replication
After a new tenant DB was created in a SAP HANA Multitenant Database
Containers system running with SAP HANA system replication, a backup of this
new tenant DB is necessary. Otherwise the replication for this tenant DB will not
start.
5.2
Disable system replication
5.2.1 Using SAP HANA cockpit 2.0
On the stopped secondary system (see above) click on the System Replication tile
in the system overview page:
In the System Replication Overview – now showing that “All services are offline” –
click on “Unregister Secondary System”:
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How To System Replication for SAP HANA
Depending whether your system should be online or offline after the unregister
command, check or uncheck the checkbox “Start system after unregistration” and
hit “OK”:
On primary system: Disable system replication on the primary system by clicking
on the system replication tile:
On the System Replication Overview click on “Disable System Replication”:
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How To System Replication for SAP HANA
Verify that you want to disable system replication by clicking “OK”:
Afterwards the former primary system reports, that System Replication is not
configured:
5.2.2 Using SAP HANA studio
Stop the secondary system with right mouse-click on Secondary System 
Configuration and Monitoring  Stop System
On secondary system: Unregister system replication for the secondary system
with right mouse-click on Secondary System  Configuration and Monitoring 
Configure System Replication … :
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How To System Replication for SAP HANA
On primary system: Disable system replication on the primary system with right
mouse-click on Primary System  Configuration and Monitoring  Configure
System Replication …:
5.2.3 Using command line tool hdbnsutil
Stop the secondary system:
sapcontrol –nr <instance_number> -function StopSystem HDB
On secondary system unregister the secondary system:
hdbnsutil -sr_unregister
If you want to use this secondary as a normal SAP HANA installation from now on,
you have to start it to complete the unregistration. On the secondary execute:
sapcontrol –nr <instance_number> -function StartSystem HDB
On primary system disable system replication:
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How To System Replication for SAP HANA
hdbnsutil -sr_disable
5.3
Setting up Multitier System Replication
As of HANA 1.0 SPS07 with the Multitier System Replication, a synchronous
system replication can be used as the source for asynchronous replication in a
chained setup of primary site, tier-2 secondary site and tier-3 secondary site.
Overview of Multitier System Replication
Until HANA 1.0 SPS11 the primary system had to synchronously replicate to the
tier-2 secondary system and the tier-2 secondary had to asynchronously15
replicate to the tier-3 secondary system.
As of HANA 1.0 SPS11 more combinations of replication modes (SYNC, SYNCMEM,
and ASYNC) in a multitier landscape are possible. For details please have a look at
SAP Note 2303243 where the supported combinations are listed.
Tier 1 to Tier 2
SYNC
SYNC
SYNC
SYNCMEM
SYNCMEM
SYNCMEM
ASYNC
Tier 2 to Tier 3
SYNC
SYNCMEM
ASYNC
SYNC
SYNCMEM
ASYNC
ASYNC
Supported since
SPS12
SPS12
SPS07
SPS11
SPS12
SPS07
SPS11
Supported replication mode combinations in Multitier System Replication
Caution
In Multitier System Replication the operation mode must be the same for all
sites. However, if the Active/Active (read enabled) operation mode
logreplay_readaccess is used between tier-1 and tier-2, only operation
mode logreplay can be used between tier-2 and tier-3!
15
Currently only asynchronous replication is supported for the connection between the tier 2 and the tier 3 secondary site.
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How To System Replication for SAP HANA
Given a running 2-tier system replication (as described above) the following steps
are to be executed to add the tier-3 secondary; this third site must fulfill the same
prerequisites as described in 4.1.
5.3.1 Using SAP HANA cockpit 2.0
Use the SAP HANA cockpit to add a tier-3 secondary to a system replication
landscape.
All three systems are registered in the SAP HANA cockpit.
Click on the HANA database that is currently configures as tier-2 secondary of the
existing 2-tier system replication landscape.
On the system overview page click on the “System Replication” tile to access the
system replication application:
Enable this tier-2 secondary to function as the source for the added tier-3
secondary by clicking on “Configure System Replication”:
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How To System Replication for SAP HANA
The Site Name is already known from topology. Simply click on “Configure”:
To stop the to-be tier-3 secondary from the system overview page of this HANA
database go via the “Overall Database Status” tile to the “Manage Services”
application:
Stop the tier-3 secondary-to-be system:
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How To System Replication for SAP HANA
Register the tier-3 secondary by clicking on the “System Replication” tile and then
hitting “Register Secondary System”:
Type a site name for the tier-3 secondary, choose replication mode (in this
example async), choose operation mode (in this example: logreplay) and enter
the tier-2 secondary system’s master host name:
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How To System Replication for SAP HANA
Once the secondary system is automatically started the replication process to the
tier-3 secondary will also start automatically.
5.3.2 Using SAP HANA studio
Use the SAP HANA studio to add a tier-3 secondary to a system replication
landscape:
Right mouse-click on the tier-2 secondary  Configuration and Monitoring 
Configure System Replication … .
Check the radio button to enable system replication – site name is already known
from topology:
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How To System Replication for SAP HANA
Stop the tier-3 secondary system with right mouse-click  Configuration and
Monitoring  Stop System:
Register the tier-3 secondary: Right mouse-click on tier-3 secondary system 
Configuration and Monitoring  Configure System Replication …
Type a logical name for the tier-3 secondary, choose replication mode ASYNC, the
same operation mode as for the primary and tier-2 secondary (in this example:
logreplay) and enter the tier-2 secondary site’s host name:
Once the secondary system is automatically started the replication process to the
tier-3 secondary will also start automatically.
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How To System Replication for SAP HANA
5.3.3 Using command line tool hdbnsutil
1. Tier-2 secondary: hdbnsutil –sr_enable
2. Tier-3 secondary: sapcontrol –nr <instance_number> -function
StopSystem HDB
3. Tier-3 secondary:
hdbnsutil -sr_register --remoteHost=<tier_2_host>
--remoteInstance=<instance number>
--replicationMode=<sync|syncmem|async>
–-operationMode=<delta_datashipping|logreplay>
--name=<siteName>
4. Tier-3 secondary: sapcontrol –nr <instance_number> -function
StartSystem HDB
5.4
Enabling full sync replication
As of HANA 1.0 SPS08 to reach a true RPO=0 for synchronous system replication,
the full sync option can be enabled for SYNC replication mode (i.e. not for
SYNCMEM). With the activated full sync option, transaction processing on the
primary blocks when the secondary is currently not connected and newly created
log buffers cannot be shipped to the secondary site. This behavior ensures that no
transaction can be locally committed without shipping the log buffers to the
secondary site.
The full sync option can be switched on and off using the command
hdbnsutil -sr_fullsync --enable|--disable
It changes the setting of the global.ini file accordingly:
global.ini/[system_replication]/enable_full_sync
However, in a running system, full sync might not become active immediately. This
is done to prevent the system from blocking transactions immediately when
setting the parameter to true. Instead, in a first step, full sync has to be enabled by
the administrator. In a second step it is internally activated, when the secondary is
connected and becomes ACTIVE.
In the M_SERVICE_REPLICATION system view the setting of the full sync option
can be viewed in the column “FULL_SYNC”. It can have the following values:


DISABLED: full sync is not configured at all
global.ini/[system_replication]/enable_full_sync = false
ENABLED: full sync is configured, but it is not yet active, so transactions do
not block in this state. To become active the secondary has to connect and
REPLICATION_STATUS has to be ACTIVE.
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How To System Replication for SAP HANA

ACTIVE: full sync mode is configured and active. If a connection of a
connected secondary is getting closed, transactions on the primary side will
block in this state.
If full sync is enabled when an active secondary is currently connected, the
FULL_SYNC will be immediately set to ACTIVE.
Note
Resolving a blocking situation of the primary caused by the enabled full sync
option must be done with the hdbnsutil command, since also a
configuration changing command could block in this state.
5.5
Change replication mode
The replication mode can be changed without having to go through a full data
shipping from the primary to the secondary afterwards.
Command on online or offline Secondary:
hdbnsutil -sr_changemode --mode=sync|syncmem|async
If the mode was changed correctly can be checked in the
M_SERVICE_REPLICATION view or with this command:
hdbnsutil -sr_state --sapcontrol=1
6.
Takeover
6.1
Perform Takeover
The following steps are performed:


Trigger a takeover to the secondary system in the event of a disaster.
Register the former primary system as new secondary when it becomes
available again.
The takeover can be triggered from SAP HANA cockpit, from the command line or
from the SAP HANA Studio.
6.1.1 Using SAP HANA cockpit 2.0
On secondary system overview page click on the “System Replication” tile:
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How To System Replication for SAP HANA
Perform a takeover by selecting “Take Over”:
Afterwards this system is running as the active HANA database not functioning as
a secondary anymore.
When the former primary is available again it can be registered as secondary.
Stop original (former) primary system.
On original (former) primary system: Register system as new secondary by
clicking the System Replication tile on this new to-be secondary and then clicking
on “Register Secondary System”:
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How To System Replication for SAP HANA
Add the site name of the original (former) primary’s site, the replication and
operation mode and the master host name of the former secondary (now primary)
and click on “Configure”:
Afterwards the roles are switched: The former primary now runs as secondary to
the new primary, which is the former secondary after takeover.
6.1.2 Using SAP HANA studio
On secondary system: Perform a takeover with right mouse-click on Secondary
System  Configuration and Monitoring  Configure System Replication …:
When the former primary is available again it can be registered as secondary.
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How To System Replication for SAP HANA
Stop original (former) primary system.
On original (former) primary system: Register system as secondary with right
mouse-click on former Primary System  Configuration and Monitoring 
Configure System Replication … :
You will be informed that this system used to be the primary system before.
6.1.3 Using command line tool hdbnsutil
1. Perform a takeover on the secondary:
hdbnsutil –sr_takeover
2. When the former primary is available again it can be registered as the new
secondary:
hdbnsutil -sr_register --remoteHost=<new primary hostname>
--remoteInstance=<instance number>
--replicationMode=<sync/syncmem/async>
--operationMode=<delta_datashipping|logreplay|logreplay_readaccess>
--name=<siteName>
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How To System Replication for SAP HANA
6.2
Client connection recovery
To perform the takeover only on the SAP HANA system will, in most cases, not be
enough. Somehow the client or application server needs to be able to continuously
reach the SAP HANA system, no matter which site is currently the primary.
There are several methods:

IP redirection: A virtual IP address is assigned to the virtual host name. In
case of a takeover, the virtual IP will unbind from the network adapter of the
primary system and bind to the adapter on the secondary system.
 DNS redirection: In this scenario the IP for the host name in the DNS will be
changed from the address of the primary to the address of the secondary
system.
Both methods have their advantages but it will be mostly decided by the IT policies
and existing configuration. If there are no existing constraints, IP redirection has
the clear benefit of being faster to process in a script rather than synchronizing
changes of DNS entries over a global network.
Since HANA 1.0 SPS09 SAP HANA offers the so-called HA/DR providers which are
capable of informing external entities about activities inside SAP HANA scale-out
(such as Host Auto-Failover) and SAP HANA system replication setups. In a
Python script actions can be defined which should be executed before or after
certain HANA activities (like startup, shutdown, failover, takeover,
connectionChanged, ...). One example for these so-called hooks is moving virtual
IP addresses after takeover in SAP HANA system replication.
Additionally external cluster management software can be used to perform the
client reconnect after takeover.
7.
Resync optimization
Whenever the primary and the secondary sites are disconnected (e. g. due to
network problems, a temporarily stopped primary or secondary, or after a
takeover and prior to a failback where the former primary is registered as new
secondary), the replication is out of sync. To get in sync again after reconnect the
SAP HANA system replication tries to achieve this by initiating a delta shipping of
the missing data (instead of a full data shipping).
Depending on the chosen operation mode (delta_datashipping or one of the
logreplay* modes) two different techniques are in place to achieve this: Data
Retention and Log Retention.
7.1
Data Retention
In the SAP HANA system replication operation mode “delta_datashipping” the
primary sends the incremental data to resync after a disconnect or for a failback, if
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How To System Replication for SAP HANA
the last snapshot, that was successfully sent to the secondary, is still available.
How long it is kept depends on the value of the parameter
datashipping_snapshot_max_retention_time (default: 300 minutes16). If it
is not available anymore, a full set of data is necessary to get in sync again.
7.2
Log Retention
In the SAP HANA system replication operation mode “logreplay” the secondary
system only uses the log of the online log area of the primary for re-syncing. After
the reconnect or a failback the primary sends the incremental log. Thus, the log
must be retained for a longer time (i. e. longer than in delta_datashipping
operation mode); log segments will not be freed, while the secondary is
disconnected.
7.2.1 Log Retention for Secondary Disconnect (on primary)
The primary will not reuse log segments in the online log area that are required to
sync the secondary via delta log shipping.
If the secondary is disconnected – but still registered

the log segments are retained on the primary and marked as RetainedFree
until secondary has successfully synced again

the log volume will grow on the primary site, until it has filled up with log
segments
In HANA studio this can be monitored on the primary system using tab Volumes by
selecting the corresponding log volume:
Once the secondary system reconnects and has synced the missing log, these log
segments are set to Free and can be reused17 afterwards.
16
As of HANA 2.0 SPS00 this default was increased from 120 minutes in lower versions.
17 Log segments marked as "Free" can be reclaimed to free the disk space of these currently unused log segments
using this console command: hdbcons –e <service> “log release”.
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How To System Replication for SAP HANA
Depending on the setting of the parameter logshipping_max_retention_size
a full log volume can be prevented at the price of a possibly necessary full data
shipping when the system reconnects.
This behavior is automatically turned on, if a secondary system with operation
mode logreplay or logreplay_readaccess is registered.
Caution
If a secondary system is shut down and not used for a longer period of
time unregister (hdbnsutil -sr_unregister18) it to prevent log
volumes from filling up on the primary site! You can unregister it using
the HANA cockpit System Replication app, the HANA studio, or the
command line.
7.2.2 Log Retention for Failback (on secondary)
On the secondary site, log retention is required to do a failback with optimized data
synchronization. The primary periodically creates persistence snapshots during
replication (every 20 min resp. 5 GB) and provides the log position information to
the secondary. After takeover, when the old primary is started as secondary, the
most recent snapshot is opened on the old primary and the missing log – up to this
snapshot – is requested from the new primary.
Log retention can occur in two situations:

While replication is active
18
Please also check SAP Note 1945676 - Correct usage of hdbnsutil -sr_unregister
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How To System Replication for SAP HANA
•
•
•

The secondary keeps all log starting from the last snapshot position
provided by the primary site
The old log is automatically released after a new snapshot has been
created on the primary site
This is active by default and ensures that during replication only a few
RetainedFree segments are kept online needed to fill the gap between
the primary snapshot and the current potential takeover log position
After a takeover
• The new primary has to keep the log until a new secondary site is
registered and has synced the missing log
• Because syncing can take some time this behavior has to be explicitly
turned on by setting this parameter on the new primary
global.ini/[system_replication]/enable_log_retention = on
Caution
If the old primary will not be reused as new secondary (failback), it should be
disabled after the takeover (hdbnsutil -sr_disable) to prevent log
volumes from filling up on the new primary site. You can disable it with SAP
HANA cockpit, SAP HANA studio, or via command line.
Note
If you have a setup in which there will be frequent failbacks between two
sites, we recommend that you set the following parameter on both sites to
simplify configuration:
global.ini/[system_replication]/enable_log_retention = on
7.2.3 Log Retention Parameters
There are two ini parameters to be mentioned in the context of log retention with
operation mode logreplay in global.ini/[system_replication] section:

enable_log_retention = auto|on|off
– auto
o Enable log retention on primary for re-connect
o Enable log retention on secondary during replication
(consider last primary snapshot position)
o Disable log retention on secondary after takeover
– On
o Enable log retention always
 required after takeover for failback with delta log shipping

logshipping_max_retention_size = 1048576 (MB), default: 1 TB
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How To System Replication for SAP HANA
o Specifies how the system behaves when many log segments of type
RetainedFree are created
o Maximum amount of log that will be kept on primary side for syncing
a system replication secondary system:
o Soft limit if set <> 0
 If the limit is reached, segment in state RetainedFree are reused
in disk full; then a full data shipping is required, i. e. the sedondary
needs to be newly registered (sr_register)
o Hard limit if set to 0
 Primary standstill, in case disk on primary runs full
7.2.4 Maximum Retention Time Estimation
How long will your system configured with SAP HANA system replication and
operation mode logreplay “survive” the above described disconnect situations
(secondary disconnect, failback) before running into a log full situation? This
question can be answered by the SQL statement
LogShipping_RetentionTime_Rev110+ contained in SAP Note 1969700 (SQL
statement collection for SAP HANA).
When executed on your primary system it provides an output like this:
The output columns provide the following information:
RETENTION_SIZE_GB: Configured log retention size (GB) – according to
parameter logshipping_max_retention_size
LOG_BACKUP_SIZE_PER_DAY_GB: Max. log backup size per day (per host and service),
average of last week
Maximum number of hours logs can be retained
Maximum number of hours until a log full situation is reached
when created redo logs can no longer be reused
LOG_FULL_DEVICE_ID: DB Internal Device responsible for first expected log full
situation
RET_SIZE_HOURS:
LOG_FULL_HOURS:
8.
Active/Active (read enabled) secondary
Since HANA 2.0 SPS00 the SAP HANA system replication can be configured as
Active/Active (read enabled) landscape where the SQL ports on the tier-2
secondary are open for read access.
This allows to actively make use of the secondary system, which in earlier HANA
revisions could not be accessed via SQL, but purely functioned as passive
replication site prepared for a fast takeover. Reporting load can be taken from the
primary system and executed on the secondary system in such an Active/Active
(read enabled) configuration.
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How To System Replication for SAP HANA
8.1
Active/Active read-only specifics
The following applies for an Active/Active (read enabled) secondary system:
• Secondary allows read-only access, no write accesses resulting in redo logging
is possible
• All replication modes (sync, syncmen, async) are supported
• The secondary must have the same HANA version as the primary (i. e. read-only
access to secondary is not supported during Near Zero Downtime Upgrade
[see below])
• Exporting tables is supported with CSV file as target (but no binary export is
available)
• The Redo Log Replay on the secondary system runs asynchronously to the
primary operations. Thus, the secondary system provides statement level
snapshot isolation19 with a delayed view on the data and no minimum delay
guarantee
• The secondary system allows read accesses via SQL. The XS service port
remains closed until a takeover took place.
• The secondary will not accept new connections if the primary is down in HANA
2.0 SPS00. Existing connections can continue.
• Single Host and scale-out HANA systems are supported
• No read support in Dynamic Tiering services in HANA 2.0 SPS00
8.2
Check Active/Active configuration
You can check, if your system replication is configured as an Active/Active (read
enabled) system using command line tools, SAP HANA cockpit and SAP HANA
studio.
8.2.1 Using the command line
As <sid>adm on command line, run one of the following commands and look for
the operation mode logreplay_readaccess.
systemReplicationStatus.py:
python $DIR_INSTANCE/exe/python_support/systemReplicationStatus.py
--sapcontrol=1 | grep OPERATION_MODE
service/ld4144/30207/OPERATION_MODE=logreplay_readaccess
service/ld4144/30201/OPERATION_MODE=logreplay_readaccess
service/ld4144/30203/OPERATION_MODE=logreplay_readaccess
hdbnsutil:
19 This is the isolation level Commited Read where different statements in a transaction may see different snapshots of the database, i.e.
each statement sees changes that were committed when execution of the statement started.
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How To System Replication for SAP HANA
hdbnsutil -sr_state | grep "operation mode"
operation mode: logreplay_readaccess
8.2.2 Using SAP HANA cockpit 2.0
On the primary system check the System Replication tile in the system overview
page:
If you open the system overview page of the read enabled secondary system you
are informed about this fact that this is a “Read-only” system. Additionally the
delay (ms) is shown on top, indicating how far the consistent view on the data on
this secondary system is behind the current data of the primary system.
Some of the monitoring tiles deliver data about the state of this secondary system,
like Memory Usage, CPU Usage, Disk Usage, active Threads, … Additionally, on the
System Replication tile you can also see the operation mode.
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How To System Replication for SAP HANA
8.2.3 Using HANA studio
On the primary system select from the monitoring view M_SYSTEM_REPLICATION
and check column “OPERATION_MODE”:
8.3
Connection types
There are two ways to execute SQL queries on the read enabled secondary
system: opening up an explicit connection to the secondary or executing an SQL
statement on the primary which is redirected to the secondary according to a hint.
Applications making use of this feature need to go the one way or the other.
8.3.1 Explicit read-only connection to secondary
The application can directly connect to the read enabled secondary system and
execute the SQL queries against it.
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How To System Replication for SAP HANA
Direct connection to read enabled secondary
You can do that for example using the SAP HANA studio simply by opening an SQL
console on the read enabled secondary system. Alternatively you can use hdbsql
when logged on as <sid>adm to select on the read enabled secondary.20
8.3.2 Statement routing from primary to secondary
You can also pass the SQL query to the primary and add a hint saying that this
statement should be preferably executed on the read enabled secondary system.
HINT-based statement routing to read enabled secondary
For such a hinted statement the HANA client opens a second connection to the
read enabled secondary system according to host information returned by
primary. The client then sends the statement to the secondary. If the secondary
20 Currently the HANA cockpit is not yet capable of accessing the read enabled secondary.
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How To System Replication for SAP HANA
cannot execute a statement for any reason it returns an error and the client sends
the statement to the primary (automatic failback).
With the so-called RESULT_LAG hint ‘hana_sr’ you can also provide a maximum
acceptable snapshot delay in <seconds>:
RESULT_LAG('hana_sr', <seconds>)
Examples of such hinted SELECT statements are:
SELECT * FROM T1 WITH HINT( RESULT_LAG ('hana_sr') );
SELECT * FROM T1 WITH HINT( RESULT_LAG ('hana_sr', 60) );
For further details please have a look at the SAP HANA SQL and System Views
Reference guide – section: Hints for Active/Active (Read-Enabled).
9.
Testing
The test phase is a very important phase to verify if KPIs are met and the
landscape performs the way it was configured. Therefore, a few test cases are
suggested below as guideline, which should be enhanced by your specific
requirements. The tests should be performed with realistic data load and size.
Test case
Description
Full
Replication
Measure how long the initial synchronization takes, from when
replication is started until primary and secondary are in sync.
Lost
Connection
Measure how long it takes until primary and secondary are
back in sync after the connection is re-established.
Takeover
Measure how long it takes for the secondary system to be fully
available after a takeover command.
Data
Consistency
Create or change data, then perform a takeover and check if
the data is still available.
Client
Reconnect
Test client access after a take-over, to check if the DNS/Virtual
IP switch worked.
Primary
becomes
secondary
Measure how long it takes until both systems are in sync, when
the former primary becomes the secondary after a takeover.
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How To System Replication for SAP HANA
10. Operation / Maintenance
There are multiple ways to monitor SAP HANA, which are described in the SAP
HANA Administration Guide and SAP Solution Manager21.
And there are various ways to verify if the primary and secondary systems are in
sync and are running correctly.
10.1.1
Alerts
With HANA 1.0 SPS09 system replication specific alerts were introduced (they are
no longer hidden behind “Internal Events”):
 System Replication Connection Closed (Alert ID 78)
 System Replication Configuration Parameter Mismatch (Alert ID 79)
As of HANA 1.0 SPS12 a new system replication specific alert was introduced for
systems running in operation mode “logreplay”:
 System Replication Logreplay Backlog (Alert ID 94)
The alert is thrown when logreplay is delayed on the secondary site causing
a longer takeover time.
The alert has a different priority based on the size of the redo log that was
not yet replayed:
– LOW
for 10 GB
– MEDIUM
for 50 GB
– HIGH
for 500 GB
These alerts are only visible with the Embedded Statistics Server (ESS)22; however,
old style alerts are still generated in order not to invalidate any reporting
infrastructure after migration. Old alerting can be disabled by setting the following
configuration parameter in global.ini:
[system_replication]
keep_old_style_alert = false (default=false)
How to configure e-mail notifications of alerts, please follow the instructions in the
SAP HANA Admin guide (see Configure E-Mail Notifications for Alerts).
As the monitoring of the secondary site was improved by the introduction of the
so-called proxy views (see below in section “Monitoring the secondary site”) with
HANA 1.0 SPS12 an alerting for the secondary site(s) was established. On the
primary site alerts occurring on the secondary hosts are shown as alerts and
associated with the host where they occurred by providing this host:port
information.
21
22
For SAP Solution Manager please consider Note 1747682 - SolMan 7.1: Managed System Setup for HANA
Migration of the classic statistics server to the Embedded Statistics Server is described in SAP note 1917938.
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How To System Replication for SAP HANA
In this example a secondary host23 reported a DiskFull event:
HANA Cockpit:
HANA studio:
23
A DB admin currently must know which host belongs to which site.
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How To System Replication for SAP HANA
10.2 Verification
10.2.1
Using SAP HANA cockpit 2.0
Since HANA 2.0 SPS00 with the XSA based SAP HANA cockpit24 you can monitor
multiple HANA systems within one cockpit. When opening the HANA cockpit for
one HANA database an extended system replication monitoring application is
offered.
If system replication is configured, the corresponding tile appears on the main
screen of the system overview page providing information about the type of
landscape (2-tier or 3-tier), the replication mode(s) between the primary and the
secondary(s), the operation mode as well as an overall replication status:
…
If all tiers are shown in green and the System Replication tile25 tells you “All
services are active and in sync” your system is doing well. Red tiers would indicate
a problem with the replication. And if you are accessing one of the secondary
HANAs with the cockpit system overview, this tile shows the other tiers in blue and
the one you are on in green.
To check the status of replication in detail, click on the System Replication tile. The
application provides an overview on the system replication configuration and
status. On top, the “chain” of systems with their replication modes is shown
containing further information about the sites and the network connections
between them.
24
More information on SAP HANA Cockpit can be found here:
http://help.sap.com/hana/SAP_HANA_Administration_Guide_en.pdf
25 If the tile does not show up, you have to grant the system replication role to the corresponding user, e. g. in the HANA
studio right mouse-click on the corresponding user in the landscape overview under Security  on the “Granted Roles tab”
click on “+”  filter for “sysrep” and select corresponding role.
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How To System Replication for SAP HANA
A graphical representation of your system replication landscape is given. It tells
you the chosen site names, the replication mode used between the sites and even
provides a snapshot view on the current average redo log shipping time ( “ Log
Buffer Write Wait Time in ms”) and the average size of shipped redo log buffers. It
describes how long it took on average to send redo log buffers of “Avg. Log Buffer
Size” to the secondary site based on measurements of the last 24 hours. 26
Below there is a selection of tabs providing more detailed information for different
system replication relevant topics.
Related Alerts tab
If a system replication relevant alert occurred, the first tab is the “Related Alerts”
tab (if no alert exists which is relevant for system replication, this tab is not
shown):
Replicated Services tab
When activating the “Replicated Services” tab an excerpt of the monitoring view
M_SERVICE_REPLICATION is shown. The displayed table shows at a glance per
site and service the replication state per service.
For synchronous replication, this is the round trip time for sending the redo log buffer and receiving the acknowledgement;
for asynchronous replication it refers to the time, it takes, until the log buffer was sent after its creation.
26
50
How To System Replication for SAP HANA
Tip
If you want to have a look at the trace files of all sites of your system
replication landscape, just click on the lower right button “View trace and
diagnostic files” on the primary’s system overview page in HANA cockpit.
This makes all diagnosis files from the trace directories of all sites visible in
the browser:
Trace file viewer in HANA cockpit
If you click on one row, you can see the details for the corresponding service
grouped thematically, like in the below example for one indexserver: Since this
information is “context aware”, you only get the information required for this
system. Thus, since this example system is running in operation mode “logreplay”
no information on delta data shipping is shown here. But the context sensitive
information about the “log replay delay” is displayed. The delta between “Last Log
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How To System Replication for SAP HANA
Position” and “Replayed Log Position” indicates how far the log replay is behind on
the secondary.
Network tab
If the “network” tab is activated – you can select the network connection you want
to analyze (pull down menu for Network Site 1 to 2, Network Site 2 to 3). A graph
appears comparing the local write wait time (i.e. writing redo log buffer into the
local log volume) with the remote write wait time (i.e. shipping the redo log and
receiving the acknowledgement) monitored over the last 24 hours. At a glance, one
can see if peak times occurred and how the network connection reacted.
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How To System Replication for SAP HANA
If the ASYNC replication mode is configured between two sites, like in this example
between tier-2 and tier-3, you also receive information about the network
performance by selecting the corresponding connection between tier-2 and tier-3:
Here the “Avg. Write Wait Time ms” describes the time it took from the creation of
the redo log buffer (i.e. committing a write transaction) until the redo log buffer in
fact was sent out to the network. This value is an indicator for peak load phases
and could point to network or I/O problems27 on the secondary site, which can
influence the primary’s performance as well.
Log Replay tab
This “Log Replay” tab is only visible, if the operation mode logreplay or
logreplay_readaccess is configured for the system replication landscape.
When this tab is activated for a secondary (selectable via pull-down menu) the log
replay delay on the secondary system is show as size in GB for the last 24 hours.
And if at some point in time the threshold of the corresponding alert (ID 94 System Replication Logreplay Backlog) was exceeded, this is indicated accordingly
(like in the below example):
If the receiving OS buffer on the secondary cannot write down the incoming redo log buffers to disk due to I/O problems,
this buffer can run full and is not able to accept newly shipped buffer fast enough.
27
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How To System Replication for SAP HANA
How to analyze a high replay backlog is described in this SAP Note 2409671 - High
replay backlog on HANA System Replication Secondary Site.
10.2.2 Using SAP HANA studio
Check the overall status on the primary’s Overview tab. This should state “All
services are active and in sync”:
To check the status of the replication in detail: Select Landscape tab  system
replication (shows information from system view M_SERVICE_REPLICATION with
a lot of columns):
For all services, the REPLICATION_STATUS should be “ACTIVE”. Detailed
information about shipped sizes and shipping times are available.
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How To System Replication for SAP HANA
10.2.3 Check via SQL query
Or directly get system replication specific information from the system view
M_SERVICE_REPLICATION. On the primary execute:
select * from "SYS"."M_SERVICE_REPLICATION";
Since HANA 1.0 SPS09 the contents of the view M_SERVICE_REPLICATION are
collected by the statistics server every hour. Thus, the history of data and log
replication can be viewed in the table. On the primary execute the following
command to view the data replicated by the indexservers (volume 4 in this
example) from the primary to the tier-2 secondary:
select * from "_SYS_STATISTICS"."HOST_SERVICE_REPLICATION"
where volume_id=4 and site_id=1;
Since HANA 1.0 SPS11 there is the new system view M_SYSTEM_REPLICATION
providing general system replication relevant information about the whole system,
e. g. which replication mode is used, which operation mode, and as which “TIER” a
site is configured. In the below example SiteA with SITE_ID=1 is currently
configured as TIER=1 (i. e. as primary). On the primary execute:
select * from "SYS"."M_SYSTEM_REPLICATION";
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How To System Replication for SAP HANA
10.2.4 Using command line tool hdbnsutil
To view the system replication topology configuration status on both systems,
execute hdbnsutil –sr_state on the primary and the secondary:
tedadm@ld2131:/usr/sap/TED/HDB07> hdbnsutil -sr_state
checking for active or inactive nameserver ...
System Replication State
~~~~~~~~~~~~~~~~~~~~~~~~
mode: primary
site id: 1
site name: SITEA
Host Mappings:
~~~~~~~~~~~~~~
ld2131 -> [SITEA] ld2131
ld2131 -> [SITEB] ld2132
done.
For a Multitier System Replication the mappings of all three sites are displayed:
ut1adm@ld2131:/usr/sap/UT1/HDB01> hdbnsutil -sr_state
checking for active or inactive nameserver ...
System Replication State
~~~~~~~~~~~~~~~~~~~~~~~~
mode: primary
site id: 1
site name: SITEA
Host Mappings:
~~~~~~~~~~~~~~
ld2131 -> [SITEA] ld2131
ld2131 -> [SITEC] ld2133
ld2131 -> [SITEB] ld2132
done.
When using the additional option –-sapcontrol=1 the key-value-pair output can
be parsed by a script line by line.
Here is the output where the -sr_state command was executed on a primary
site of a Multitier System Replication:
ut1adm@ld2131:/usr/sap/UT1/HDB01> hdbnsutil -sr_state --sapcontrol=1
checking for active or inactive nameserver ...
SAPCONTROL-OK: <begin>
mode=primary
site id=1
site name=SITEA
mapping/ld2131=SITEA/ld2131
mapping/ld2131=SITEC/ld2133
mapping/ld2131=SITEB/ld2132
SAPCONTROL-OK: <end>
Done
Here is the output where the -sr_state command was executed on a tier-2
secondary site of a Multitier System Replication:
ut1adm@ld2132:/usr/sap/UT1/HDB01> hdbnsutil -sr_state --sapcontrol=1
checking for active or inactive nameserver ...
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How To System Replication for SAP HANA
SAPCONTROL-OK: <begin>
mode=sync
site id=2
site name=SITEB
active primary site=1
mapping/ld2132=SITEA/ld2131
mapping/ld2132=SiteC/ld2133
mapping/ld2132=SITEB/ld2132
primary masters=ld2131
SAPCONTROL-OK: <end>
done.
Further explanation of the output:






mode – can have the values primary, sync, async, and syncmem to
represent the mode relevant on the site where the command is executed (e.
g. in a Multitier System Replication on the primary the mode would be
primary, on the tier-2 secondary it could be either sync or syncmem, and
on the tier-3 secondary it is async).
site id – is a unique identifier of a site which is incremented for each site
attached to a SAP HANA system replication. It is first removed, when the
system replication is disabled.
site name – is the name you give your sites during the enable and register
steps of system replication configuration.
mapping/<currentHost> – shows which hosts are involved in this SAP
HANA system replication together with their site name; if the HANA
database is offline, this host mapping cannot be shown on the secondaries.
active primary site – shows the site id of the currently active site.
primary masters – shows the hostname(s) of the currently active
master candidates of the primary28.
Starting with HANA 1.0 SPS12 and Rev112.03 when running “hdbnsutil –
sr_state” on an offline HANA, no host mapping will be available anymore.
Please refer to SAP note 2315257 for more details.
10.3 System Replication status checks
There are some ways to gather information about the overall status of the sites
and of the system replication.
IMPORTANT: In a Multitier System Replication on tier-3 the given “primary” is the tier-2 secondary – which from this
perspective is the primary for this tier-3.
28
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How To System Replication for SAP HANA
10.3.1
Using landscapeHostConfiguration.py
Check the overall status of the primary system using as <sid>adm OS user the
script landscapeHostConfiguration.py (located in $DIR_INSTANCE/
/exe/python_support).
<sid>adm># python $DIR_INSTANCE/exe/python_support/landscapeHostConfiguration.py
|
|
|
|
|
Host
|
|
----- |
host1 |
host2 |
Host
Active
-----yes
yes
|
|
|
|
|
Host
Status
-----ok
ok
|
...
| NameServer |
|
| Config Role|
| --------- | ---------- |
|
...
| master 1
|
|
...
| master 2
|
NameServer
Actual Role
----------master
slave
|
...
|
| -----|
...
|
...
overall host status: ok
The following host states are possible:




OK: System is OK.
WARNING: A host auto-failover to a standby host is taking place.
INFORMATION: The landscape is completely functional, but the current
(actual) role of the host differs from the configured role.
ERROR: There are not enough active hosts.
Please use the parameter "--sapcontrol=1", if you require a reliable and
parsable output:
<sid>adm># python $DIR_INSTANCE/exe/python_support/landscapeHostConfiguration.py -sapcontrol=1
SAPCONTROL-OK: <begin>
host/ld2131/hostActualRoles=worker
host/ld2131/removeStatus=
host/ld2131/nameServerConfigRole=master 1
host/ld2131/failoverStatus=
host/ld2131/hostConfigRoles=worker
host/ld2131/failoverActualGroup=default
host/ld2131/storageConfigPartition=1
host/ld2131/host=ld2131
host/ld2131/indexServerConfigRole=worker
host/ld2131/failoverConfigGroup=default
host/ld2131/storageActualPartition=1
host/ld2131/indexServerActualRole=master
host/ld2131/nameServerActualRole=master
host/ld2131/hostActive=yes
host/ld2131/hostStatus=ok
host/ld2131/storagePartition=0
host/ld2132/hostActualRoles=worker
host/ld2132/removeStatus=
host/ld2132/nameServerConfigRole=master 3
host/ld2132/failoverStatus=
host/ld2132/hostConfigRoles=worker
host/ld2132/failoverActualGroup=default
host/ld2132/storageConfigPartition=2
host/ld2132/host=ld2132
host/ld2132/indexServerConfigRole=worker
host/ld2132/failoverConfigGroup=default
host/ld2132/storageActualPartition=2
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How To System Replication for SAP HANA
host/ld2132/indexServerActualRole=slave
host/ld2132/nameServerActualRole=slave
host/ld2132/hostActive=yes
host/ld2132/hostStatus=ok
host/ld2133/hostActualRoles=standby
host/ld2133/removeStatus=
host/ld2133/nameServerConfigRole=master 2
host/ld2133/failoverStatus=
host/ld2133/hostConfigRoles=standby
host/ld2133/failoverActualGroup=default
host/ld2133/storageConfigPartition=0
host/ld2133/host=ld2133
host/ld2133/indexServerConfigRole=standby
host/ld2133/failoverConfigGroup=default
host/ld2133/storageActualPartition=0
host/ld2133/indexServerActualRole=standby
host/ld2133/nameServerActualRole=slave
host/ld2133/hostActive=yes
host/ld2133/hostStatus=ignore
overall_status=ok
SAPCONTROL-OK: <end>
10.3.2
Using systemReplicationStatus.py
Check the overall status of the system replication using as <sid>adm OS user the
script systemReplicationStatus.py (located in $DIR_INSTANCE/
/exe/python_support).
<sid>adm># python $DIR_INSTANCE/exe/python_support/systemReplicationStatus.py
| Host
|
| Service Name
|
| Site Name | Secondary
|
| Host
|
|
...
| Replication |...
| Status
|
| ------ | ---------------- | --------- | --------- | ----- | ----------- |--| ld7805 | indexserver
| WALLDORF | ld8475
| ... | ACTIVE
|
| ld8513 | statisticsserver | WALLDORF
| ld8513 | xsengine
| WALLDORF
| ld8476
| ld8476
|
|
| ACTIVE
| ACTIVE
|
|
| ld8513 | nameserver
| ld8513 | indexserver
| WALLDORF
| WALLDORF
| ld8476
| ld8476
|
|
| ACTIVE
| ACTIVE
|
|
| ld8559 | indexserver
| WALLDORF
| NOT MAPPED |
|
|
status system replication site "2": ACTIVE
status system replication site "3": ACTIVE
overall system replication status: ACTIVE
Local System Replication State
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mode: PRIMARY
site id: 1
site name: WALLDORF
The script provides the following return codes.
10:
11:
12:
13:
14:
15:
No System Replication
Error
Unknown
Initializing
Syncing
Active
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How To System Replication for SAP HANA
10.3.3 Using console
To check the replication status on all hosts and for all services the HDB console
can be used. Especially in case of ASYNC replication this will provide some
additional information currently not shown by the system view, because in this
mode the primary does not await the acknowledgement upon arrival of the shipped
redo log buffer.
In this case an option is to check the current log position on the secondary using
hdbcons on the secondary side – where this information is not available via SQL –
on each node and for each persistency relevant service29:
<sid>adm># hdbcons -e hdbindexserver "replication info"
SAP HANA DB Management Client Console (type '\?' to get help for client
commands)
Try to open connection to server process 'hdbindexserver' on system 'M19',
instance '19'
SAP HANA DB Management Server Console (type 'help' to get help for server
commands)
Executable: hdbindexserver (PID: 66110)
[OK]
-listing default statistics for volume 3
System Replication Secondary Information
========================================
System Replication Secondary Configuration
[system_replication] site_id
= 2
[system_replication] site_name
= SiteA
[system_replication] mode
= sync
[system_replication] operation_mode
= logreplay
[system_replication] datashipping_min_logsize_threshold
= 5368709120
[system_replication] datashipping_min_time_interval
= 600
[system_replication] reconnect_time_interval
= 30
[system_replication] enable_log_compression
= false
[system_replication] preload_column_tables
= true
[system_replication] ensure_backup_history
= true
[system_replication] enable_ssl
= off
[system_replication] keep_old_style_alert
= false
[system_replication] enable_log_retention
= 1
[system_replication] logshipping_max_retention_size
= 1048576
Last Primary Host: ld2133
Last Primary Port: 32003
Log Connection
- ptr
: 0x00007fd58931a400
- channel
: NetworkChannel FD 25 [0x00007fd5ad064a98]
idx=2} 10.96.4.20/65117_tcp->10.96.4.22/32003_tcp Connected,[r---]
{refCnt=3,
- mode
: ReplicationMode_Synchronous
- logSinceLastBackup : 663552 bytes
- timeSinceLastBackup : 67431655 microseconds
Data Connection
29 The service can be passed to “hdbcons” by providing the service name with the option “-e <service>”, like hdbnameserver,
hdbindexserver, etc. In MultiDB HANAs, however, the service is to be passed via its PID using the option “-p
<PID_of_service>”. You get the PID of the corresponding service for example running “HDB proc” as user <sid>adm on OS
commandline.
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How To System Replication for SAP HANA
- ptr
: 0x00007fd589315000
- channel
: NetworkChannel FD 31 [0x00007fd5ad064c58]
idx=3} 10.96.4.20/65118_tcp->10.96.4.22/32003_tcp Connected,[----]
Secondary Statistics
- Creation Timestamp
- Last Reset Timestamp
- Statistic Reset Count
{refCnt=2,
: 08.12.2015-14.25.27 (1449584727282603)
: 08.12.2015-14.25.27 (1449584727282603)
: 0
- ReplicationMode
- OperationMode
: sync
: logreplay
-
ReplicationStatus
ReplicationStatusDetails
ReplicationFullSync
shippedLogPos
shippedLogPosTimestamp
sentLogPos
sentLogPosTimestamp
shippedLogBuffersCount
shippedLogBuffersSize
shippedLogBuffersSizeUsed
shippedLogBuffersSizeNet
shippedLogBufferDuration
shippedLogBufferDurationMin
shippedLogBufferDurationMax
shippedLogBufferDurationSend
shippedLogBufferDurationComp
shippedLogBufferThroughput
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
DISABLED
0x641cbb00
08.12.2015-14.59.17 (1449586757965706)
0x0
01.01.1970-00.00.00 (0)
11241
8335585280 bytes
8309875456 bytes (99.69%)
8309875456 bytes (99.69%)
0 microseconds
0 microseconds
0 microseconds
0 microseconds
0 microseconds
0.00 bytes/s
-
replayFinishLogPos
replayFinishLogPosTimestamp
replayStartLogPos
replayPushLogPos
replayRetentionLogPos
replayStepCount
replayLogSize
replayDuration
:
:
:
:
:
:
:
:
0x641cbb00
08.12.2015-14.59.17 (1449586757965706)
0x641cbb00
0x641cbb00
0x62a66fcb
61709
8335581056 bytes
111608005 microseconds
ReplicationStatus_Active
- shippedSavepointVersion
- shippedSavepointLogPos
- shippedSavepointTimestamp
: 2252
: 0x5c595f82
: 08.12.2015-14.25.28 (1449584728678668)
-
shippedFullBackupCount
shippedFullBackupSize
shippedFullBackupSizeNet
shippedFullBackupDuration
shippedFullBackupDurationComp
shippedFullBackupThroughput
:
:
:
:
:
:
1
17884512256 bytes
17884512256 bytes (100.00%)
81098893 microseconds
0 microseconds
220527205.67 bytes/s
-
shippedLastFullBackupSize
shippedLastFullBackupSizeNet
shippedLastFullBackupStart
shippedLastFullBackupEnd
shippedLastFullBackupDuration
:
:
:
:
:
17884512256 bytes
17884512256 bytes (100.00%)
08.12.2015-14.25.28 (1449584728678668)
08.12.2015-14.26.49 (1449584809777561)
81098893 microseconds
-
shippedDeltaBackupCount
shippedDeltaBackupSize
shippedDeltaBackupSizeNet
shippedDeltaBackupDuration
shippedDeltaBackupDurationComp
shippedDeltaBackupThroughput
:
:
:
:
:
:
0
0 bytes
0 bytes (-nan%)
0 microseconds
0 microseconds
0.00 bytes/s
- shippedLastDeltaBackupSize
- shippedLastDeltaBackupSizeNet
: 0 bytes
: 0 bytes (-nan%)
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How To System Replication for SAP HANA
- shippedLastDeltaBackupStart
- shippedLastDeltaBackupEnd
- shippedLastDeltaBackupDuration
-
: not set
: not set
: 0 microseconds
Secondary sync'ed via Log Count : 0
syncLogCount
: 0
syncLogSize
: 0 bytes
Secondary Backup History
: complete
shippedMissingLogCount
: 0
shippedMissingLogSize
: 0 bytes
backlogSize
: 0 bytes
backlogTime
: 0 microseconds
backlogSizeMax
: 0 bytes
backlogTimeMax
: 0 microseconds
- Secondary
- Secondary
- Secondary
- Secondary
- Secondary
- Secondary
- Secondary
- Secondary
[OK]
-[EXIT]
-[BYE]
Log Connect time
Data Connect time
Log Close time
Data Close time
Log Reconnect Count
Log Failover Count
Data Reconnect Count
Data Failover Count
:
:
:
:
:
:
:
:
08.12.2015-14.25.27 (1449584727296916)
08.12.2015-14.25.27 (1449584727491743)
not set
not set
0
0
0
0
Here you get information about the used replication and operation modes (mode,
operation_mode). You see which IP address is used for data and log transfer
(Log connection and Data connection) and – since this system replication
example is running with operation mode logreplay – you can see how far the log
replay is hanging behind the shipped log on this secondary (the delta between
shippedLogPos and replayFinishLogPos30). For all services the
ReplicationStatus should be ReplicationStatus_Active.
10.3.4 Using predefined SQL statement
Attached to this SAP Note 1969700 is a set of complex SQL statements –
including some system replication relevant statements.
The statements contained in the text files can simply be copied and executed from
some client.
30 For this specific topic please also refer to the SAP HANA system replication FAQ SAP Note 1999880 – question: How can I
determine the current log replay delay?
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How To System Replication for SAP HANA
In this example the “System Replication Bandwidth” SQL copied to and executed
in the HANA cockpit “Execute SQL” application:
Additionally the zip file can be imported to and executed in the SAP HANA studio
as follows:
For the primary system go to the System Information tab and right-click on the
“Name” column  Import SQL Statements.
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How To System Replication for SAP HANA
Select the “SQL Statements.zip” you downloaded from the SAP note:
A folder with the SQL statements will be imported. Right-click on the statements
under Replication  Overview and Executed a statement – for example the
Overview:
You will receive a lot of information about the system replication landscape and the
per service replication state:
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How To System Replication for SAP HANA
Of interest are for example the “Local log buffer write throughput (MB/s)”
compared to the “Log buffer shipping throughput (MB/s)” in synchronous
replication. For synchronous replication this could for example be an indication for
network problems or a problem with the I/O on the secondary side (for SYNC), if
these two values differ too much.31
10.4 Monitoring and replicating ini parameter changes
ini parameters basically should be the same on the primary and secondary
system and are checked automatically. The configuration parameter checker
reports differences between primary and secondary if parameters differ.
In the “Alerts” tile on the system overview page of HANA cockpit you can click on
“Show All” to see all alerts – including the ones created for “parameter mismatch”:
31 For details on this please refer to the HowTo https://scn.sap.com/docs/DOC-58553 on system replication network
configuration.
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How To System Replication for SAP HANA
Also in the “Alerts” tab in HANA studio you can see the generated alerts:
Since HANA 1.0 SPS12 you can activate ini parameter replication, where changes
made on the primary are automatically replicated to the secondary sites.
ini parameter checks:
 Are done every hour by default.
 Generate alerts (visible in SAP HANA studio as internal event and the
system view M_EVENTS)32.
 Are optimized for the most recently changed parameters.
Enable and disable the ini parameter check on the primary site with
[inifile_checker]/enable = true|false (default: true)
Enable and disable the ini parameter replication on the primary site with
[inifile_checker]/replicate = true|false (default: false)
32
How you can setup an e-mail notification is described in the SAP HANA Admin guide in section: Configure E-Mail
Notifications for Alerts.
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How To System Replication for SAP HANA
The ini parameter replication follows these rules:
Parameter set on
Primary
Secondary
Set
Not set
Not set
Set
Set to value x
Set to value y
Action
Copy parameter to secondary
Delete parameter on the secondary
Copy value x to secondary
In the global.ini an exclusion list can be maintained to exclude parameters to
be checked or replicated. Just follow the syntax to define exclusion rules for
certain parameters:
exclusion_[inifile name|*][/] = [section with
wildcards|*][/parameter with wildcards|*], ... :=
SYSTEM\|HOST\|TENANT\|\*
If for example you intend to use your secondary system for DEV/QA systems and
set the global allocation limit to its minimal value (as described above), you may
exclude this parameter global_allocation_limit from these checks like this:
[inifile_checker]
enable = true
interval = 3600
exclusion_global.ini/SYSTEM =
memorymanager/global_allocation_limit
10.5 Monitoring the secondary site
Since HANA 1.0 SPS11 there is a possibility to monitor the secondary site using socalled proxy views. They provide remote SQL access on the primary – through
proxy schemas and views – allowing for monitoring and reporting of secondary site
statistics (for any replication mode). During registration of a secondary system,
the new proxy schema on the primary site is created for each registered secondary
site. The schema follows the naming convention _SYS_SR_SITE_<siteName>
and contains a selected subset of monitoring views, which proxies the statistics
from the secondary site. Proxy views have the same column definitions as the
equivalently named public synonyms already available for the primary. When a
secondary site is unregistered the corresponding schema will be dropped.
In the HANA cockpit on the system overview page for the primary click on
“Execute SQL” to get to the SAP HANA Database Explorer. Then open the
primary’s “Catalog” and go to the corresponding schema:
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How To System Replication for SAP HANA
Proxy views of the secondary site’s monitoring views (HANA cockpit)
In the HANA studio in the landscape overview just open the Catalog and the
corresponding schema:
Proxy views of the secondary site’s monitoring views (HANA studio)
There are some limitations of proxy views which need to be considered:
•
Monitoring view access is only possible if primary and secondary sites run with
exactly the same software version.
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How To System Replication for SAP HANA
•
When such a proxy view is queried against and the secondary site is not
started, no results are shown without the report of an SQL error.
•
Querying against SAP HANA multitenant database containers landscapes is
limited to single tenant databases or the system database, meaning there are
no views unifying all tenants on the system database similar to the
SYS_DATABASES schema.
As of HANA 2.0 SPS00 and only if the system replication is configured as
Active/Active (read enabled) system using the operation mode
“logreplay_readaccess” even more data of the secondary systems are
available in the proxy schema _SYS_SR_SITE_<siteName>. Making use of the
read access to the secondary system many of the other monitoring views of the
secondary can be made accessible via virtual tables.
In the SAP HANA Database Explorer for the primary system (after clicking on
“Execute SQL” on the system overview page) open the proxy schema and click on
the “tables”item. A long list of accessible monitoring views from the secondary is
shown:
Virtual tables available in the proxy schema
of the secondary system (HANA cockpit)
Equally you can access these virtual tables with the SAP HANA studio:
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How To System Replication for SAP HANA
Virtual tables available in the proxy schema
of the secondary system (HANA studio)
Any of these proxy views or virtual tables can be accessed via SQL from the primary
simply by providing the correct secondary’s schema name, for example:
select * from "_SYS_SR_SITE_SiteB"."M_HOST_INFORMATION";
Note
Based on these views and tables available in the proxy schema the statistics
server is able to generate alerts on the secondary sites (identified by
host:port) of a system replication landscape.
10.6 System replication connection
The replication in a configured system replication uses either a public or a separate
network channel between the involved data centers.33
10.6.1 Secure configuration of the connection
By default the primary and secondary systems establish communication using the
internal host names34.
With an IPaddress–virtualHostname mapping on the involved sites the
system replication hostname resolution can be set configuring a separate network
for system replication data traffic between primary and secondary35.
This is done in the section [system_replication_hostname_resolution] in
global.ini, where all hosts of the primary and the secondary sites have to be
defined on each site:
Please also check the HowTo guides on system replication networks: https://scn.sap.com/docs/DOC-56044 and
https://scn.sap.com/docs/DOC-58553
34 All SAP HANA system views containing a HOST column show these internal host names, e. g. M_DATABASE.
35 As mentioned, in Multitier System Replication the tier 2 secondary serves as primary for the replication to the tier 3
secondary.
33
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How To System Replication for SAP HANA
global.ini/[system_replication_hostname_resolution]
<ip-address_same_site>=<internal_host_same_site>
<ip-address_other_site>=<internal_host_other_site>
This also holds valid for a multitier system replication consisting of three sites
(primary, tier-2 secondary and tier-3 secondary) because roles can switch after
takeovers and failbacks.
Note
The parameters in the global.ini file must be set prior to registering the
secondary system, because the hdbnsutil -sr_register command uses
this mapping. Registration is one step in the process of configuring the
secondary system.
The entries in the [system_replication_hostname_resolution] section are
used in combination with the listeninterface parameter in the
[system_replication_communication] section. The following combinations
are possible:
[system_replication_
communication]
listeninterface
.global
.global
.internal
[system_replication_
hostname_resolution]
Additional Information
No mappings specified
Default if nothing is specified. The default
network route is used for system replication communication.
This is normally the public network.
Entries for the primary and
secondary hosts (for all
hosts in multitier setups)
Entries for the primary and
secondary hosts
Caution
If you use a public network instead of a
separate network, you must secure this
connection with additional measures such
as a firewall or a virtual private network
and/or SSL.
A separate network is used for system
replication communication.
Tip
This way you can use a separate network
for multitier system replication.
A separate network is used for system
replication communication. The primary
hosts listen on the dedicated ports of the
separate network only and incoming
requests on the public interfaces are
rejected.
Caution
In SAP HANA 1.0 SPS 11, network
communication for system replication
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How To System Replication for SAP HANA
with listeninterface=.internal is
supported for two-tier replication but not
for three-tier setups!
There are two ways to activate the [system_replication_hostname_resolution] in
your system:
1. Restart all sites after setting the parameter
2. Temporarily resolve the system replication configuration – here no restart
of the primary is necessary:
a. Stop secondary
b. Unregister secondary
c. Disable primary
d. Enable primary
e. Register secondary
f. Start secondary
Here is an example of the settings for a 2-tier system replication (3 node system)
using a separate internal network per site and a separate connection for the
system replication.
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How To System Replication for SAP HANA
Multi-node SAP HANA System Replication over separate network
with separate internal network
10.6.2
Allowed senders for the connection
If for some reason no separate network channel was configured for the SAP HANA
system replication communication between the involved sites, the parameter
allowed_sender could be used to restrict communication between primary and
secondary to certain hosts. For this, the following settings can be configured in the
global.ini file on the primary site:
global.ini/[system_replication_communication]
Parameter: allowed_sender
Value:
<list of IP-addresses of secondary or CIDR-netmasks>
Example:
10.0.1.0/30
The default is no restriction.
10.6.3 Encryption of the connection
SAP HANA System Replication supports secure network communication (SSL) for
Data and Log shipping to the secondary site. The following settings can be
configured in the global.ini file:
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How To System Replication for SAP HANA
global.ini/[system_replication_communication]
Parameter: enable_ssl
Values:
off:
ssl is disabled for source and target replication channels (default)
on:
ssl is enabled for source and target replication channels
source: ssl is enabled for source replication channels only
target: ssl is enabled for target replication channels only
The encrypted communication requires a certificate available in the internal store.
The keystore (key.pem) and truststore (trust.pem) are located in
/usr/sap/<SID>/HDB<nr>/<host>/ssl
Differentiating between source and target is especially helpful for 3-tier
configurations. The topology transfer uses the encryption as supported with the
secure HANA internal host communication.
10.6.4 Data and Log compression for transfer
Since HANA 1.0 SPS09 compression can be configured to reduce the amount of
traffic between sites especially over long distances. It will be used for the initial full
data shipping, the sub sequential delta data shipping as well as for the continuous
log shipping.
Configuration is done in global.ini on the secondary site.
[system_replication]
enable_log_compression = true (default = false)
enable_data_compression = true (default = false)
By default content compression is turned off; log buffer tail compression (default =
true) and log buffer content compression can be combined.
10.6.5
Monitoring the connection
The connection between the primary and the secondary system should be
available for replication. If this is not the case for a certain time, the redo log
cannot be shipped to the secondary system, the log segments start piling up on
the primary (see Log Retention section), the secondary system is not takeover
ready.
For the primary to stay operational at all times, even if the connection is lost
occasionally, an internal event is generated which is visible as an internal event
alert in the SAP HANA cockpit, the SAP HANA studio and in the system view
M_EVENTS (if the old – not embedded – statistics server is used). With HANA 1.0
SPS09 system replication a specific alert was introduced (as described above in
the “Alerts” section):
 System Replication Connection Closed (Alert ID 78)
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How To System Replication for SAP HANA
Additionally the replication connection can be checked using the HDB console:
hdbcons -e hdbindexserver "replication info"
The output delivers “Log Connection” information for the connection used by the
provided service. It also shows errors if the connection cannot be resolved
properly:
…
Log Connection
- ptr
: 0x00007fdb6e8e3410
- channel
: NetworkChannel FD 158
[0x00007fdb6f1bbc90] {refCnt=3, idx=1} 10.68.91.226/3
0103_tcp->10.68.92.13/49537_tcp Connected,[r---]
...
Use the OS command
lsof –n –p <indexserver-pid>
to check, if the configured connection is actually used. The output delivers “Log
Connection” information for the connection used by the provided service.
For a more detailed analysis of the network connection used for system replication
refer to the “Troubleshoot System Replication” chapter in the
SAP_HANA_Troubleshooting_and_Performance_Analysis_Guide_en.pdf.
10.7 Upgrade and Maintenance
If for some reason you have to stop and restart the primary or the secondary, once
the systems are available they will automatically try to get in sync again. There are
no manual steps necessary.
Caution
If the system is running with operation mode “logreplay” or
“logreplay_readaccess” please check the section on “Log Retention” in
this document to prevent your system from running full or having to do a full
data shipping, in case the time the primary could not replicate becomes too
long.
Note
To avoid a full data shipping after the upgrade to get both systems in sync
again, refer to the sections “Data Retention” and “Log Retention”.
Depending on the settings of the logshipping_max_retention_size and
datashipping_snapshot_max_retention_time parameter settings
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How To System Replication for SAP HANA
and the time the upgrade is taking, an optimized resync with delta data or
log shipping can be achieved.
System Replication with SAP HANA 2.0 requires authentication for data and log
shipping channels. The authentication is done using the certificates in the system
PKI SSFS store. Thus, there is an additional manual setup step required to
exchange certificates in the system PKI SSFS store between primary and
secondary site when upgrading to HANA 2.0 (please refer to SAP Note 2369981 as
well.)
10.7.1
“Normal” Upgrade
Due to the fact that the version of the secondary system must be higher or the
same as the one running on the primary system you always have to upgrade the
secondary first.
The process is straightforward:
1. Upgrade the secondary system and wait until the upgrade is done
./hdblcm --action=update
2. Upgrade the primary system and wait until the upgrade is done
./hdblcm --action=update
Caution
If you are upgrading from HANA 1.0 to HANA 2.0. proceed as follows instead:
1. Upgrade the secondary system and wait until the upgrade is done
./hdblcm --action=update --hdbupd_server_nostart
2. Upgrade the primary system and wait until the upgrade is done
./hdblcm --action=update
3. Copy the systemPKI SSFS key and data file from the primary to the
secondary; these files can be found here:
$DIR_INSTANCE/../global/security/rsecssfs/data/SSFS_<SID>.DAT
$DIR_INSTANCE/../global/security/rsecssfs/key/SSFS_<SID>.KEY
4. Start the secondary system.
After both systems are available again they will get in sync automatically.
10.7.2 Near Zero Downtime Upgrade
System replication can be used for a Near Zero Downtime Upgrade (NZDU), where
first the secondary is upgraded, then it takes over operation from the original
primary (via takeover), and afterwards the primary is upgraded. In a failback the
original primary is attached as new secondary to re-establish the system
replication.
Caution
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How To System Replication for SAP HANA
With HANA 2.0 SPS00 the Active/Active (read enabled) operation mode
“logreplay_readaccess” can be configured. One important restriction is
that primary and secondary system must have the exact same HANA
version. Thus, during NZDU no read access is possible after the secondary
was upgraded and is getting in sync again with the primary before it will
take over!
The process, which is described in detail in the SAP HANA Administration Guide
looks like this:
1. Set user store entry for automatic repository import at takeover time on
primary and secondary by executing the following command, where
<myUser>36 requires the necessary privileges to import the repository
content of the new version of the software during the takeover:
hdbuserstore SET SRTAKEOVER <public hostname>:<sqlport>
<myUser> <myUsersPasswd>
2. Upgrade secondary system
./hdblcm --action=update
3. Wait until secondary is in sync as shown in the M_SERVICE_REPLICATION
view
4. Stop primary system and perform takeover to the secondary (new primary)
Caution
If you are upgrading from HANA 1.0 to HANA 2.0 copy the systemPKI
SSFS key and data file from this current primary to the new to-besecondary; these files can be found here:
$DIR_INSTANCE/../global/security/rsecssfs/data/SSFS_<SID>.DAT
$DIR_INSTANCE/../global/security/rsecssfs/key/SSFS_<SID>.KEY
5. Upgrade the previous primary system without starting the system
./hdblcm --action=update --hdbupd_server_nostart
Caution
Depending on the setting of the INI parameter
datashipping_snapshot_max_retention_time and the duration
between the takeover step (4) and the following registration step (6) a full
data shipping or a delta shipping will be necessary to get the systems in
36
How to create a user <myUser> with the privileges required for importing the repository content is shown in the following
example:
CREATE USER MY_REPO_IMPORT_USER PASSWORD MyRepoUserPW123;
GRANT EXECUTE ON SYS.REPOSITORY_REST TO MY_REPO_IMPORT_USER;
GRANT REPO.READ ON ".REPO_PACKAGE_ROOT" TO MY_REPO_IMPORT_USER;
GRANT REPO. IMPORT TO MY_REPO_IMPORT_USER;
GRANT SELECT ON _SYS_REPO.DELIVERY_UNITS TO MY_REPO_IMPORT_USER;
GRANT REPO.ACTIVATE_IMPORTED_OBJECTS ON ".REPO_PACKAGE_ROOT" TO MY_REPO_IMPORT_USER;
77
How To System Replication for SAP HANA
sync again. As of HANA 2.0 the default setting is 300 minutes; thus you
have 5 hours’ time between the steps (4) and (6).
6. Register the previous primary as secondary
./hdbnsutil –sr_register …
7. Start the previous primary as secondary
To achieve a real zero downtime upgrade from the ABAP application server
perspective, please have a look at this SAP Note 1913302 (Connectivity suspend of
Appserver during takeover).
Tip
For the procedure to upgrade a Multitier System Replication in a NZDU
manner, please refer to SAP Note 2386973 (Near Zero Downtime
Upgrades for HANA database 3-tier System Replication)
10.7.3 Hardware Exchange
Additionally, as described in SAP Note 1984882 (Using HANA system replication
for Hardware Exchange with Minimum Downtime) hardware can be exchanged
with a minimal downtime using SAP HANA system replication. The procedure is
very similar to the described NZDU.
11. Further documentation
11.1
Whitepapers and HowTo guides
SAP HANA High Availability
whitepaper
http://scn.sap.com/docs/DOC-60334
SAP HANA in Data Centers
http://scn.sap.com/docs/DOC-60341
HowTo Perform System
Replication for SAP HANA
https://scn.sap.com/docs/DOC-47702
SAP HANA Network Requirements
whitepaper
https://scn.sap.com/docs/DOC-63221
HowTo: Network required for SAP
HANA system replication
https://scn.sap.com/docs/DOC-56044
HowTo: Configure Network
Settings for HANA System
Replication
https://scn.sap.com/docs/DOC-58553
SAP HANA Memory Usage
explained
SAP Note 190823 - SAP HANA
Storage
http://scn.sap.com/docs/DOC-60337
http://service.sap.com/sap/support/notes/1900823
78
How To System Replication for SAP HANA
SAP HANA Host Auto-Failover
whitepaper
SAP HANA Academy
11.2
http://scn.sap.com/docs/DOC-62494
http://scn.sap.com/community/hana-inmemory/blog/2015/06/15/sap-hana-multitenantdatabase-container-mdc-videos-now-available-onthe-sap-hana-academy
Official Guides
SAP HANA Administration Guide
http://help.sap.com/hana/SAP_HANA_Administration_G
uide_en.pdf
SAP HANA LCM Tools Reference
http://help.sap.com/hana/SAP_HANA_LCM_Tools_Refer
(hdblcm, ...)
ence_Guide_en.pdf
SAP HANA Master Guide
SAP HANA Security Guide
SAP HANA server installation
http://help.sap.com/hana/SAP_HANA_Master_Guide_en.
pdf
http://help.sap.com/hana/SAP_HANA_Security_Guide_e
n.pdf
http://help.sap.com/hana/SAP_HANA_Server_Installatio
n_Guide_en.pdf
SAP HANA SQL and System Views
http://help.sap.com/hana/SAP_HANA_SQL_and_System_
Reference
Views_Reference_en.pdf
SAP HANA Technical Operations
http://help.sap.com/hana/SAP_HANA_Technical_Operati
Manual
ons_Manual_en.pdf
SAP HANA Troubleshooting and
http://help.sap.com/hana/SAP_HANA_Troubleshooting_
Performance Analysis Guide
and_Performance_Analysis_Guide_en.pdf
79
www.sap.com/contactsap
www.sdn.sap.com/irj/sdn/howtoguides
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