Switching Over and Switching Back

Switchover and Switchback is the process in which active and passive roles are exchanged between the Master and Replica servers, so that if the Master is currently active, it changes to passive after Switchover passes the active role to the Replica. If the Replica is active, it changes to passive after Switchover passes the active role to the Master. Switchover can be triggered at the push of a button or automatically by CA ARCserve RHA when it detects that the Master is unavailable, if you enabled the Perform Switchover Automatically option from the Switchover and Reverse Initiation dialog. When this option is Off, the system notifies you that the Master server is down so you can manually initiate switchover from the CA ARCserve RHA Manager.

This section contains the following topics:

How Switchover and Switchback Work

Initiate Switchover

Initiate Switchover for a Group

Initiate Switchback

Initiate Switchback for a Group

Recover Active Server

Recover Active Server for a Distributed Group

Switchover Considerations

How Switchover and Switchback Work

After the HA scenario starts running and the synchronization process is completed, the Replica checks the Master on a regular basis, by default every 30 seconds, to see if it is alive. There are three types of monitoring checks:

• Ping -- a request sent to the Master to verify that the Master is up and responding
• Database check -- a request that verifies the appropriate services are running and all databases are mounted and SharePoint websites are started.
• User-defined check -- a custom request you can tailor to monitor specific applications

If an error occurs with any part of the set, the entire check is considered to have failed. If all checks fail throughout a configured timeout period (by default, 5 minutes), the Master server is considered to be down. Then, depending on the HA scenario configuration, CA ARCserve HA sends you an alert or automatically initiates a switchover.

When you created an HA scenario, you defined how you want the switchover to be initiated.

• If you selected the Initiate Switchover manually option from the Switchover and Reverse Replication Initiation page, perform a manual switchover. For more information, refer to the topic, Initiate Switchover.
• If you selected the Initiate Switchover automatically option, you can still perform a manual switchover, even if the Master is alive. You can initiate switchover when you want to test your system, or you want to use the Replica server to continue the application service while some form of maintenance is performed on the Master server. Triggered (automatic) switchover is in all ways identical to manual switchover performed by the administrator, except it is triggered by a resource failure on the master server rather than by an administrator manually initiating the switchover by clicking the Perform Switchover button. Server ping response, application service status, and database connectivity are monitored. The timeout parameters are configurable and are more extensively covered in the CA ARCserve RHA Administration Guide.

When you created an HA scenario, you defined how you want the reverse scenario to be initiated.

• If you selected the Initiate Reverse Replication automatically option from the Switchover and Reverse Replication Initiation page, replication in the reverse direction (from Replica to Master) automatically begins after a switchover, one the original Master server becomes available again.
• If you selected the Initiate Reverse Replication manually option, you need to perform switchback manually. If you select the manual option and do not initiate a manual switchback, you must resynchronize data from Replica to Master, even after testing a clean switchover without a Master failure.

When the Reverse Replication feature is off, to start reverse replication after a switchover has occurred, click the Run button. The benefit to this feature is, if both the master and replica servers were online and connected during switchover, resynchronization in the reverse direction is not required. Resynchronization involves comparing the data on the master and replica servers to determine which changes to transfer before real-time replication starts; this can take some time. If automatic reverse replication is turned on, and both servers were online during switchover, replication is reversed without the need for resynchronization. This is the one situation in which resynchronization is not required.

Initiate Switchover

Once triggered, whether manually or automatically, the switchover process itself is fully automated.

Note: Though the following steps show Exchange scenario screens as examples, the procedure is similar for all server types.

To initiate manual switchover

1. Open the Manager and select the desired scenario from the Scenario pane. Verify it is running.
2. Click on the Perform Switchover button, or select from the Tools menu the Perform Switchover option:

   A confirmation message appears.

3. Click OK on the Perform Switchover confirmation message. This procedure initiates a switchover from the Master server to the Replica server:

   Detailed information about the switchover processes is located in the Events pane during switchover.

4. After the switchover is completed the scenario stops:

   Note: The only case in which the scenario may continue to run after switchover is when automatic reverse replication is defined as Start automatically.

   In the Event pane a message appears, informing you that Switchover completed, and then that the Scenario has stopped.

   Now, the Master becomes passive and the Replica becomes active.