VERITAS Volume Manager 3.1 Administrator's Guide

Volume Manager Operations
FastResync (Fast Mirror Resynchronization)
Chapter 3116
with Release 3.1, the snapshot command behaves as before with the
exception that it creates an association between the original volume and
the snap volume. A new command, vxassist snapback, leverages this
association to expediently return the snapshot plex (M
Snap
) to the
volume from which it was snapped (in this example, V
Pri
).
Figure 3-1, FMR Enhanced Snapshot, depicts the extended transitions of
the snapshot model as introduced by the snapback and snapclear
commands.
Figure 3-1 FMR Enhanced Snapshot
Additionally, a new command, vxassist snapclear, relieves a volume
of the administrative overhead of tracking a snapshot by permanently
destroying the association created by the snapshot command. This
capability is useful in situations where it is known that a snapshot will
never return to the volume from which it was created.
Theory of Operations
The basis of FMR lies in change tracking. Keeping track of updates
V
Pri
M
Pri
V
Pri
M
Pri
M
Snap
V
Pri
M
Pri
M
Snap
V
Snap
M
Snap
V
Snap
snapstart
snapshot
snapback
snapclear
START
Extended Snapshot Model
Legend:
V
Pri
i - primary volume
M
Pri
i - mirror plex
M
Snap
- snapshot plex
V
Snap
- snap volume