How FastResync works

FastResync provides the following enhancements to VxVM:

Faster mirror resynchronization

FastResync optimizes mirror resynchronization by keeping track of updates to stored data that have been missed by a mirror. (A mirror may be unavailable because it has been detached from its volume, either automatically by VxVM as the result of an error, or directly by an administrator using a utility such as vxplex or vxassist. A returning mirror is a mirror that was previously detached and is in the process of being re-attached to its original volume as the result of the vxrecover or vxplex att operation.) When a mirror returns to service, only the updates that it has missed need to be re-applied to resynchronize it. This requires much less effort than the traditional method of copying all the stored data to the returning mirror.

Once FastResync has been enabled on a volume, it does not alter how you administer mirrors. The only visible effect is that repair operations conclude more quickly.

Re-use of snapshots

FastResync allows you to refresh and re-use snapshots rather than discard them. You can quickly re-associate (snap back) snapshot plexes with their original volumes. This reduces the system overhead required to perform cyclical operations such as backups that rely on the volume snapshots.

FastResync can be implemented in one of two ways:

Non-persistent FastResync

Non-persistent FastResync allocates its change maps in memory. The maps do not reside on disk nor in persistent store.

Persistent FastResync

Persistent FastResync keeps the FastResync maps on disk so that they can survive system reboots, system crashes and cluster crashes.

More Information

How non-persistent FastResync works with snapshots

How persistent FastResync works with snapshots