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Chapter 9. Maintenance procedures

You must apply specific steps to ensure that the cluster does not cause unplanned impact so that you can perform maintenance of different components of SAP HANA system replication HA environments.

Use maintenance procedures to keep your cluster in a healthy state during planned change activity or to restore the health after unplanned incidents.

9.1. Cleaning up the failure history
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Clear any failure notifications from the cluster that may be there from previous testing. This resets the failure counters and the migration thresholds.

Procedure

  1. Clean up resource failures: 

    [root]# pcs resource cleanup

  2. Clean up the STONITH failure history: 

    [root]# pcs stonith history cleanup

Verification

  • Check the overall cluster status and confirm that no failures are displayed anymore: 

    [root]# pcs status --full

  • Check that the stonith history for fencing actions has 0 events: 

    [root]# pcs stonith history

9.2. Triggering a HANA takeover using cluster commands
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Use the cluster control to execute a simple takeover of the primary site to the secondary site.

For detailed steps, refer to the section Testing the setup - Triggering a HANA takeover using cluster commands.

9.3. Updating the operating system and HA cluster components
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For updates or offline changes on the HA cluster, the operating system or even the system hardware, you must follow the Recommended Practices for Applying Software Updates to a RHEL High Availability or Resilient Storage Cluster.

9.4. Performing maintenance on the SAP HANA instances
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For any kind of maintenance of applications or other components that the HA cluster manages, you must enable the cluster maintenance mode to prevent the cluster from any interference during the maintenance.

During the update of your HANA instances, the cluster remains running, but is not actively monitoring resources or taking any actions. After the change on the HANA instances is done, it is vital to refresh the cluster resource status and verify that the detected resource states are all correct. Only then you can safely disable the maintenance mode without unexpected cluster actions.

If you need to stop the cluster for the maintenance activity, ensure that you set maintenance mode first, then stop and start the cluster on the node as required for the HANA maintenance.

Prerequisites

  • You have configured the Pacemaker cluster to manage the HANA system replication.

Procedure

  1. Set maintenance mode for the entire cluster: 

    [root]# pcs property set maintenance-mode=true

    Setting maintenance for the whole cluster ensures that no activity during the maintenance phase can trigger cluster actions and impact the HANA update process.

  2. Verify that the cluster resource management is fully disabled: 

    [root]# pcs status
...
              *** Resource management is DISABLED ***
  The cluster will not attempt to start, stop or recover services

Node List:
  * Online: [ dc1hana1 dc1hana2 dc2hana1 dc2hana2 ]

Full List of Resources:
  * Clone Set: cln_SAPHanaTop_RH1_HDB02 [rsc_SAPHanaTop_RH1_HDB02] (maintenance):
    * rsc_SAPHanaTop_RH1_HDB02  (ocf:heartbeat:SAPHanaTopology):         Started dc1hana1 (maintenance)
    * rsc_SAPHanaTop_RH1_HDB02  (ocf:heartbeat:SAPHanaTopology):         Started dc1hana2 (maintenance)
    * rsc_SAPHanaTop_RH1_HDB02  (ocf:heartbeat:SAPHanaTopology):         Started dc2hana1 (maintenance)
    * rsc_SAPHanaTop_RH1_HDB02  (ocf:heartbeat:SAPHanaTopology):         Started dc2hana2 (maintenance)
  * Clone Set: cln_SAPHanaCon_RH1_HDB02 [rsc_SAPHanaCon_RH1_HDB02] (promotable, maintenance):
    * rsc_SAPHanaCon_RH1_HDB02  (ocf:heartbeat:SAPHanaController):       Promoted dc1hana1 (maintenance)
    * rsc_SAPHanaCon_RH1_HDB02  (ocf:heartbeat:SAPHanaController):       Unpromoted dc1hana2 (maintenance)
    * rsc_SAPHanaCon_RH1_HDB02  (ocf:heartbeat:SAPHanaController):       Unpromoted dc2hana1 (maintenance)
    * rsc_SAPHanaCon_RH1_HDB02  (ocf:heartbeat:SAPHanaController):       Unpromoted dc2hana2 (maintenance)
  * Clone Set: cln_SAPHanaFil_RH1_HDB02 [rsc_SAPHanaFil_RH1_HDB02] (maintenance):
    * rsc_SAPHanaFil_RH1_HDB02  (ocf:heartbeat:SAPHanaFilesystem):       Started dc1hana1 (maintenance)
    * rsc_SAPHanaFil_RH1_HDB02  (ocf:heartbeat:SAPHanaFilesystem):       Started dc1hana2 (maintenance)
    * rsc_SAPHanaFil_RH1_HDB02  (ocf:heartbeat:SAPHanaFilesystem):       Started dc2hana1 (maintenance)
    * rsc_SAPHanaFil_RH1_HDB02  (ocf:heartbeat:SAPHanaFilesystem):       Started dc2hana2 (maintenance)
  * rsc_vip_RH1_HDB02_primary   (ocf:heartbeat:IPaddr2):         Started dc1hana1 (maintenance)
  * rsc_vip_RH1_HDB02_readonly  (ocf:heartbeat:IPaddr2):         Started dc2hana1 (maintenance)

...

  3. Update the HANA instances using the SAP procedure. If you have to perform a takeover during the HANA update, you can use the SAP HANA Takeover with Handshake option. For more information see also Is it possible to use SAP HANA "Takeover with Handshake" option with the HA Solutions for managing HANA System Replication?.

    If you stop the cluster in this step, ensure that you start it again before you proceed with the next steps. Keep the maintenance mode enabled.

  4. After the HANA update, verify that the HANA system replication is working correctly. Use the systemReplicationStatus.py script to show the status of the HANA system replication on the primary site. Below is the example after a manual takeover to the secondary site during the maintenance: 

    [root]# su - <sid>adm -c "HDBSettings.sh systemReplicationStatus.py \
--sapcontrol=1 | grep -i replication_status="
service/dc2hana2/30003/REPLICATION_STATUS=ACTIVE
service/dc2hana1/30001/REPLICATION_STATUS=ACTIVE
service/dc2hana1/30007/REPLICATION_STATUS=ACTIVE
service/dc2hana1/30003/REPLICATION_STATUS=ACTIVE
site/1/REPLICATION_STATUS=ACTIVE
overall_replication_status=ACTIVE

    Before you proceed, ensure that the system replication is healthy and reported as ACTIVE.

  5. Refresh all cluster resources to execute one monitor operation and update their status: 

    [root]# pcs resource refresh
Waiting for 1 reply from the controller
... got reply (done)

    It is crucial that the HANA resources update cluster and node attributes to reflect the new HANA system replication status. It ensures that the cluster has the correct information and does not trigger recovery actions due to incorrect status information, after the maintenance stops.

  6. Check the cluster status and verify the resource status and main HANA resource score attribute. All resources must show as Started and the promotable resources must show as Unpromoted on all nodes: 

    [root]# pcs status resources
  * Clone Set: cln_SAPHanaTop_RH1_HDB02 [rsc_SAPHanaTop_RH1_HDB02] (maintenance):
    * rsc_SAPHanaTop_RH1_HDB02  (ocf:heartbeat:SAPHanaTopology):         Started dc1hana1 (maintenance)
    * rsc_SAPHanaTop_RH1_HDB02  (ocf:heartbeat:SAPHanaTopology):         Started dc1hana2 (maintenance)
    * rsc_SAPHanaTop_RH1_HDB02  (ocf:heartbeat:SAPHanaTopology):         Started dc2hana1 (maintenance)
    * rsc_SAPHanaTop_RH1_HDB02  (ocf:heartbeat:SAPHanaTopology):         Started dc2hana2 (maintenance)
  * Clone Set: cln_SAPHanaCon_RH1_HDB02 [rsc_SAPHanaCon_RH1_HDB02] (promotable, maintenance):
    * rsc_SAPHanaCon_RH1_HDB02  (ocf:heartbeat:SAPHanaController):       Unpromoted dc1hana1 (maintenance)
    * rsc_SAPHanaCon_RH1_HDB02  (ocf:heartbeat:SAPHanaController):       Unpromoted dc1hana2 (maintenance)
    * rsc_SAPHanaCon_RH1_HDB02  (ocf:heartbeat:SAPHanaController):       Unpromoted dc2hana1 (maintenance)
    * rsc_SAPHanaCon_RH1_HDB02  (ocf:heartbeat:SAPHanaController):       Unpromoted dc2hana2 (maintenance)
  * Clone Set: cln_SAPHanaFil_RH1_HDB02 [rsc_SAPHanaFil_RH1_HDB02] (maintenance):
    * rsc_SAPHanaFil_RH1_HDB02  (ocf:heartbeat:SAPHanaFilesystem):       Started dc1hana1 (maintenance)
    * rsc_SAPHanaFil_RH1_HDB02  (ocf:heartbeat:SAPHanaFilesystem):       Started dc1hana2 (maintenance)
    * rsc_SAPHanaFil_RH1_HDB02  (ocf:heartbeat:SAPHanaFilesystem):       Started dc2hana1 (maintenance)
    * rsc_SAPHanaFil_RH1_HDB02  (ocf:heartbeat:SAPHanaFilesystem):       Started dc2hana2 (maintenance)
  * rsc_vip_RH1_HDB02_primary   (ocf:heartbeat:IPaddr2):         Started dc1hana1 (maintenance)
  * rsc_vip_RH1_HDB02_readonly  (ocf:heartbeat:IPaddr2):         Started dc2hana1 (maintenance)

  7. Check the cluster attributes and verify that srHook, roles and score attributes are in the correct new state: 

    [root]# SAPHanaSR-showAttr
...

Site lpt        lss mns      opMode    srHook srMode srPoll srr
----------------------------------------------------------------
DC2  1757953883 4   dc2hana1 logreplay PRIM   sync   SOK    S
DC1  30         4   dc1hana1 logreplay SOK    sync   PRIM   P

Host     clone_state roles                        score  site sra srah version     vhost
--------------------------------------------------------------------------------------------
dc1hana1 DEMOTED     master1:master:worker:master 100    DC1  -   -    2.00.083.00 dc1hana1
dc1hana2 DEMOTED     slave:slave:worker:slave     -12200 DC1      -    2.00.083.00 dc1hana2
dc2hana1 DEMOTED     master1:master:worker:master 150    DC2  -   -    2.00.083.00 dc2hana1
dc2hana2 DEMOTED     slave:slave:worker:slave     -10000 DC2      -    2.00.083.00 dc2hana2
    • The srHook is PRIM on the node that is running the primary instance and it shows SOK on the correct secondary.
    • The srPoll attribute still shows the previous status. It will update after you remove the maintenance.
    • The score is 150 on the node where the main primary is running and 100 on the main secondary.

  8. When the checks of the previous steps show the landscape in the expected healthy state, you can remove the maintenance mode of the cluster again: 

    [root]# pcs property set maintenance-mode=

    When you lift the maintenance it triggers a monitor run of all resources again. The cluster updates the status of the promotable resources to Promoted and Unpromoted in correspondence to the location of the primary and secondary instances. The resources now also update the srPoll attribute again to match the srHook attribute value.

When you configure AUTOMATED_REGISTER=false in the SAPHanaController resource, which is the default, you must manually register the former primary site as the new secondary after takeover and start it. Otherwise, the unregistered site remains stopped.

Procedure

  1. Register the former primary site as the new secondary site. Run as user <sid>adm on one stopped former primary instance: 

    rh1adm $ hdbnsutil -sr_register --remoteHost=<node> \
--remoteInstance=${TINSTANCE} --replicationMode=sync \
--operationMode=logreplay --name=<site>
    • Replace <node> with the new primary instance host, for example, dc2hana1 if there was a takeover from dc1hana1 to dc2hana1.
    • Replace <site> with your new secondary HANA site name, for example, DC1 if dc1hana1 is to be registered as a secondary.
    • Choose the values for replicationMode and operationMode according to your requirements for the system replication.
    • $TINSTANCE is an environment variable that is set automatically for user <sid>adm by reading the HANA instance profile. The variable value is the HANA instance number.

  2. Start the secondary HANA site. Run as <sid>adm on one new secondary instance node: 

    rh1adm $ sapcontrol -nr ${TINSTANCE} -function StartSystem HDB

Verification

  • On one new primary instance, show the current status of the re-established HANA system replication. Below is the example after a takeover from dc1hana1 to dc2hana1 and DC2 is the new primary site: 

    rh1adm $ cdpy; python systemReplicationStatus.py
|Database |Host     |Port  |Service Name |Volume ID |Site ID |Site Name |Secondary |Secondary |Secondary |Secondary |Secondary     |Replication |Replication |Replication    |Secondary    |
|         |         |      |             |          |        |          |Host      |Port      |Site ID   |Site Name |Active Status |Mode        |Status      |Status Details |Fully Synced |
|-------- |-------- |----- |------------ |--------- |------- |--------- |--------- |--------- |--------- |--------- |------------- |----------- |----------- |-------------- |------------ |
|RH1      |dc2hana2 |30003 |indexserver  |        4 |      2 |DC2       |dc1hana2  |    30003 |        1 |DC1       |YES           |SYNC        |ACTIVE      |               |        True |
|SYSTEMDB |dc2hana1 |30001 |nameserver   |        1 |      2 |DC2       |dc1hana1  |    30001 |        1 |DC1       |YES           |SYNC        |ACTIVE      |               |        True |
|RH1      |dc2hana1 |30007 |xsengine     |        2 |      2 |DC2       |dc1hana1  |    30007 |        1 |DC1       |YES           |SYNC        |ACTIVE      |               |        True |
|RH1      |dc2hana1 |30003 |indexserver  |        3 |      2 |DC2       |dc1hana1  |    30003 |        1 |DC1       |YES           |SYNC        |ACTIVE      |               |        True |

status system replication site "1": ACTIVE
overall system replication status: ACTIVE

Local System Replication State
~~~~~~~~~~

mode: PRIMARY
site id: 2
site name: DC2
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