Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)
See “Enabling FastResync on a volume” on page 373.
FastResync enhancements
FastResync provides the following enhancements to VxVM:
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.
Faster mirror
resynchronization
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.
Re-use of snapshots
Non-persistent FastResync
Non-persistent FastResync allocates its change maps in memory. They do not
reside on disk nor in persistent store. This has the advantage that updates to the
FastResync map have little impact on I/O performance, as no disk updates needed
to be performed. However, if a system is rebooted, the information in the map is
lost, so a full resynchronization is required on snapback. This limitation can be
overcome for volumes in cluster-shareable disk groups, provided that at least one
of the nodes in the cluster remained running to preserve the FastResync map in
its memory. However, a node crash in a High Availability (HA) environment
requires the full resynchronization of a mirror when it is reattached to its parent
volume.
Understanding Veritas Volume Manager
FastResync
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