Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)

The FastResync feature minimizes the time and I/O needed to resynchronize the
data in the snapshot. If FastResync is not enabled, a full resynchronization of the
data is required. For more details:
See the Veritas Volume Manager Administrator's Guide.
Finally, you can use the vxassist snapclear command to break the association
between the original volume and the snapshot volume. Because the snapshot
relationship is broken, no change tracking occurs. Use this command if you do
not need to reuse the snapshot volume to create a new point-in-time copy.
The use of the vxassist command to administer traditional (third-mirror
break-off) snapshots is not supported for volumes that are prepared for instant
snapshot creation. Use the vxsnap command instead.
See “Full-sized instant snapshots” on page 202.
See “Space-optimized instant snapshots” on page 204.
Full-sized instant snapshots
Full-sized instant snapshots are a variation on the third-mirror volume snapshot
model that make a snapshot volume available for I/O access as soon as the snapshot
plexes have been created.
Figure 17-2 shows the full-sized instant volume snapshot model.
Figure 17-2
Full-sized instant snapshot creation and usage in a backup cycle
Start
Original volume
vxsnap prepare
vxsnap make
vxsnap reattach
vxsnap dis
or
vxsnap split
vxsnap refresh
Backup
cycle
Snapshot volume
Independent volume
Back up to disk, tape or other media
The snapshot volume can also be used to create a replica
database or file system when synchronization is complete.
To create an instant snapshot, use the vxsnap make command. This command
can either be applied to a suitably prepared empty volume that is to be used as
the snapshot volume, or it can be used to break off one or more synchronized
Administering volume snapshots
Full-sized instant snapshots
202