Dell PowerFlex 4.5.x Technical Overview

Accessing target volumes

There are several situations in which the target volumes are made accessible to the hosts.

• Failover — Fail over the RCG, used especially for disaster recovery. During failover, the application I/Os are stopped at the source and the access mode of the source volumes is changed to inaccessible. The target volumes are brought to the newest consistent image available on the destination and their access mode is changed to read-write. Recovery from a failed over state to a normal operation state can be achieved by either restoring the replication, or reversing it.
• Test failover — Test a failover of the RCG. This allows you to test failover mode, and provides the application with access to the target volumes, without interrupting data synchronization.
• Switchover — Switch over the RCG. Switchover is a planned failover. The application I/Os are stopped at the source and the data is synchronized so that the target volume is consistent with the source volume. The access mode of the original source volumes is changed to unavailable or read-only. The access mode of the original target volumes is changed so that the hosts can read and write to the volumes.

Target volumes can be accessed in R/W only after failover or switchover has been performed. Once the RCG is in failover or switchover mode, you can decide how to continue with replication:

• Restore replication — This maintains the replication direction from the original source and overwrites all data at the target.
• Reverse replication — This changes the direction so that the original target becomes the source. All data at the original source is overwritten by the data at the target.