This document explains How to Perform a SQL2008 push button Switchover and Switchback using CA ARCserve RHA r15.
This document is to act as a supplement to the CA ARCserve RHA r15 Replication and High Availability Operations Guide for Microsoft SQL Server included with the CA ARCserve RHA installation package.
How to Perform a SQL2008 push button Switchover and Switchback using CA ARCserve RHA r15?
- The switchover properties tab (HA Scenario only) will allow selection of CA ARCserve RHA Network Redirection Methods including DNS, Move IP and Host Rename.
- For most SQL Server installation DNS redirection only is sufficient.
- A SQL server with NetBIOS libraries loaded, or a Linked Server using windows authentication will require Host Rename with Reboot in addition to DNS redirection.
- Upon Scenario run the Time-To-Live (TTL Value) of the Master's DNS A Record is reduced from 15 minutes (Default) to 60 seconds. This will ensure clients will resolve to the Replica server after a switchover in a timely manner.
IMPORTANT: If testing in a lab environment where the scenario is started and switchover is invoked within 15 minutes of the initial scenario run, client's will not have retrieved the updated TTL Value of 60 seconds for the Master's DNA A Record and may not properly detect a switchover has occurred without flushing (ipconfig /flushdns) and re registering DNS (ipconfig /registerdns).
Waiting a minimum of 30 minutes after scenario run before testing a switchover is recommended.
- When the scenario is started the data on the master will be compared with the data on the replica (synchronization) and once the data matches at the block or file level (depending on synchronization method) replication mode will be invoked and real time changes will be sent to the replica.
- All replication traffic is sent at the byte level regardless of the synchronization method employed.
- The data set in the scenario is not secured until you see both Synchronization Finished and All modification during synchronization period are replicated within the CA ARCserve RHA Manager Events pane.
Once the data set is synchronized the CA ARCserve RHA 'Is Alive' will be invoked:
- This is a network check where the replica will ping the master node every 30 seconds for a reply.
- If a reply is not received the replica will try this for up to 5 minutes and if this time is exceeded without a response CA ARCserve RHA will alert a switchover is required. This value is user configurable within the switchover tab properties.
- In addition to the network level polling the 'Is Alive' will also check the status of the databases on the master via an ODBC database check to ensure they are online. If the application level check fails CA ARCserve RHA will alert a switchover is required.
- To perform a pushbutton switchover press the switchover icon, or go to Tools and select 'Perform Switchover'.
- A dialogue popup box will appear asking you to confirm you would like to switchover.
- The 'Run a Reverse Replication Scenario after this Switchover' checkbox when selected will immediately replicate data after the switchover completes from the active replica to the inactive master.
- This option will bypass the synchronization process as the CA ARCserve RHA engine is able to maintain synchronization throughout the switchover process.
- It is not recommended to enable this feature as there is no time permitted for the user to assess the integrity of the data on the replica before overwriting that data back to the master.
- Once the switchover is invoked the CA ARCserve RHA Manager Event console will give real time feedback of the switchover process.
The switchover process flow is as follows:
- Push button switchover is invoked.
- SQL Services are stopped on the master server.
- Any data residing in spool is sent to the replica.
- Once spool on the master reaches 0kb DNS redirection is initiated. The Host A Record of the master is modified to reflect the IP Address of the replica.
- SQL Services are started on the replica server.
- Switchover process is completed and SQL is active on replica.
- When SQL is active on the replica it will accept user queries and updates just as if it were running on the master. When ready to synchronize the data back to the inactive master the scenario is restarted via the run button.
- CA ARCserve RHA will determine which node is active and will prompt to run a backwards synchronization.
- Once started the synchronization methods will be presented. The default and recommended selection for SQL is Block Synchronization.
- Once the data set is secured back on the master both Synchronization Finished and All modification during synchronization period are replicated within the CA ARCserve RHA Manager Events pane.
- To perform a push button switchback press the switchover icon, or go to Tools and select 'Perform Switchover'.
- A dialogue popup box will appear asking you to confirm you would like to switchback.
- Switchback will be invoked following same process flow outlined in step 5. Once completed SQL will be active on the master.