Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

306 Administering volume snapshots
Cascaded snapshots
snapshot volume, S2, can be used to restore the original volume if that volume becomes
corrupted. For a database, you might need to replay a redo log on S2 before you could use
it to restore V. These steps are illustrated in Figure 9-6.
Figure 9-6 Using a snapshot of a snapshot to restore a database
If you have configured snapshots in this way, you may wish to make one or more of the
snapshots into independent volumes. There are two
vxsnap commands that you can use to
do this:
■ vxsnap dis dissociates a snapshot volume and turns it into an independent volume.
The volume to be dissociated must have been fully synchronized from its parent. If a
snapshot volume has a child snapshot volume, the child must also have been fully
synchronized. If the command succeeds, the child snapshot becomes a snapshot of
the original volume. Figure 9-7 illustrates the effect of applying this command to
snapshots with and without dependent snapshots.
Original
volume
vxsnap make source=V
Snapshot
volume of V:
vxsnap make source=S1
vxsnap restore V source=S2
Apply redo logs
1. Create instant snapshot S1 of volume V
2. Create instant snapshot S2 of S1
3. After contents of V have gone bad, apply the database redo logs to S2
4. Restore contents of V instantly from snapshot S2 and keep S1 as a stable copy
VS1
Original
volume
V
Snapshot
volume of V:
S1
Snapshot
volume of V:
S1
Snapshot
volume of V:
S1
Original
volume
V
Original
volume
V
Snapshot
volume of S1:
S2
Snapshot
volume of S1:
S2
Snapshot
volume of S1:
S2