Promotable Mirrors

Explains the use of promotable mirrors for enhanced performance, data recovery, and business continuity.

In general, mirror volumes are created for the purpose of preventing or minimizing data loss. Data loss scenarios range from accidental overwrites to rack failures, to a disaster that destroys an entire data center. Mirror volumes are also used to improve performance or to make copies of data for use in other clusters without impacting production.

As of the 4.0.2 release, all new mirror volumes can be made into read-write volumes. In addition, read-write volumes that were mirrored to other volumes can be made into mirrors (to establish a mirroring relationship in the other direction). This functionality is useful in scenarios such as:

Disaster recovery If a read-write volume with critical data goes down in a primary data center, a mirror volume in a remote data center can be made into a read-write volume in order to maintain business continuity. Later, if the primary data center comes back online, the original mirror relationship can be restored by making the new read-write volume back into a mirror volume.
Running applications on a copy of production data
Resynchronization (reestablishing a mirror relationship after it is broken)

For a hands-on tutorial on promotable mirrors, check this blog.