Using Promotable Mirrors

In general, mirror volumes are created for the purpose of preventing or minimizing data loss. Data loss scenarios range from accidental overwrites to rack failure, to a disaster that destroys an entire datacenter. 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 datacenter, a mirror volume in a remote datacenter can be made into a read-write volume in order to maintain business continuity. Later, if the primary datacenter 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)
    Note: Customers who upgrade to 5.0 need to follow some specific steps in order to use promotable mirrors for volumes that were in place before the upgrade. See Volume Upgrades in Version 5.0.

The following sections provide more information about promotable mirrors: