VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Volume Snapshots
42 VERITAS Volume Manager Administrator’s Guide
Volume Snapshots
The volume snapshotmodel isshown in “Snapshot Creation and the Backup Cycle.” This
figure also shows the transitions that are supported by the snapback and snapclear
commands to vxassist.
Snapshot Creation and the Backup Cycle
The vxassist snapstart command creates a mirror to be used for the snapshot, and
attaches it tothe volumeas asnapshot mirror. (The vxassist snapabort command can
be used to cancel this operation and remove the snapshot mirror.)
When the attachment is complete, the vxassist snapshot command is used to create a
new snapshot volume by taking one or more snapshot mirrors to use as its data plexes.
The snapshot volume contains a copy of the original volume’s data at the time that you
took the snapshot. If more than one snapshot mirror is used, the snapshot volume is itself
mirrored.
The command, vxassist snapback, can be used to return snapshot plexes to the
original volume from which they were snapped, and to resynchronize the data in the
snapshot mirrors from the data in the original volume. This enables you to refresh the
data in a snapshot after each time that you use it to make a backup. As described in
“FastResync” on page 43, you can use the FastResync feature of VxVM to minimize the
time needed to resynchronize the data in the snapshot mirror. If FastResync is not
enabled, a full resynchronization of the data is required.
Original
volume
Refresh on
snapback
snapstart
snapback
snapclear
Original
volume
Independent
volume
Back up to disk,
tape or other
medium, or use
to create replica
database or file
system.
Backup
Cycle
START
snapshot
Snapshot
volume
Snapshot
mirror