FastResync of Volume Snapshots

VxVM allows you to take multiple snapshots of your data at the level of a volume. A snapshot volume contains a stable copy of a volume's data at a given moment in time that you can use for online backup or decision support. If FastResync is enabled on a volume, VxVM uses a FastResync map to keep track of which blocks are updated in the volume and in the snapshot. If the data in one mirror is not updated for some reason, it becomes out-of-date, or stale, with respect to the other mirrors in the volume. The presence of the FastResync map means that only those updates that the mirror has missed need be reapplied to resynchronize it with the volume. A full, and therefore much slower, resynchronization of the mirror from the volume is unnecessary.

The persistent form of FastResync ensures that FastResync maps survive both system crashes and cluster restarts. When snapshot volumes are reattached to their original volumes, FastResync allows the snapshot data to be quickly refreshed and re-used. If Persistent FastResync is enabled on a volume in a private disk group, such incremental resynchronization can happen even if the host is rebooted.

Persistent FastResync can track the association between volumes and their snapshot volumes after they are moved into different disk groups. When the disk groups are rejoined, this allows the snapshot plexes to be quickly resynchronized. Non-Persistent FastResync cannot be used for this purpose.

For more information, see Volume Snapshots and FastResync.