The volume
snapshot model is shown in Figure 1-32 “Snapshot Creation and the
Backup Cycle” This figure also shows the transitions that are supported
by the snapback and snapclear commands to vxassist.
The vxassist snapstart command creates a mirror to be used
for the snapshot, and attaches it to the volume as a snapshot 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”, 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.
Alternatively, you can
use the vxassist snapclear command to break the association between
the original volume and the snapshot volume. The snapshot volume
then has an existence that is independent of the original volume.
This is useful for applications that do not require the snapshot
to be resynchronized with the original volume.
For more information about taking snapshots of a volume, see “Backing
Up Volumes Online Using Snapshots”, and the vxassist(1M) manual
page.
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