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For some applications, it may be desirable to create a snapshot of an existing snapshot as illustrated in Creating a snapshot of a snapshot.
Creating a snapshot of a snapshot
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Even though the arrangement of the snapshots in this figure appears similar to the snapshot hierarchy shown in Snapshot cascade, the relationship between the snapshots is not recursive. When reading from the snapshot S2, data is obtained directly from the original volume, V, if it does not exist in S2 itself.
Such an arrangement may be useful if the snapshot volume, S1, is critical to the operation. For example, S1 could be used as a stable copy of the original volume, V. The additional 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 Using a snapshot of a snapshot to restore a database.
Using a snapshot of a snapshot to restore a database
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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. Dissociating a snapshot volume illustrates the effect of applying this command to snapshots with and without dependent snapshots.
Dissociating a snapshot volume
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vxsnap split dissociates a snapshot and its dependent snapshots from its parent volume. The snapshot volume that is to be split must have been fully synchronized from its parent volume. This operation is illustrated in Splitting snapshots.
Splitting snapshots
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