Protecting Hyper-V Environments › Switching Over and Switching Back › How Switchover and Switchback Work

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. The following types of monitoring checks are available:

• Ping -- a request sent to the VM on the Master to verify that the VM is up and responding. If the Is Alive check returns false, the Replica brings up the VM automatically.
• User-defined check -- a custom request you can tailor to monitor specific applications.
• Connect to database -- a request sent to the Master to verify that the appropriate services are running, and the VM is active and responding to pings.

These checks are performed sequentially (if enabled). 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 VM on the Master server is considered to be down. Then, depending on the HA scenario configuration, Arcserve RHA 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 VM connectivity are monitored. The timeout parameters are configurable and are more extensively covered in the 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 resynchronization in the reverse direction is not required, if both the master and replica servers were online and connected during switchover. 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.