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353Administering volume snapshots
Creating traditional third-mirror break-off snapshots
plexes are snapped back. This task resynchronizes the data in the volume so that
the plexes are consistent.
Note: To enhance the efficiency of the snapback operation, enable FastResync
on the volume before taking the snapshot, as described in “Enabling FastResync
on a volume” on page 292.
To merge one snapshot plex with the original volume, use the following
command:
# vxassist [-g diskgroup] snapback snapshot
where snapshot is the snapshot copy of the volume.
To merge all snapshot plexes in the snapshot volume with the original volume,
use the following command:
# vxassist [-g diskgroup] -o allplexes snapback snapshot
To merge a specified number of plexes from the snapshot volume with the
original volume, use the following command:
# vxassist [-g diskgroup] snapback nmirror=number snapshot
Here the nmirror attribute specifies the number of mirrors in the snapshot
volume that are to be re-attached.
Once the snapshot plexes have been reattached and their data resynchronized,
they are ready to be used in another
snapshot operation.
By default, the data in the original volume is used to update the snapshot plexes
that have been re-attached. To copy the data from the replica volume instead,
use the following command:
# vxassist [-g diskgroup] -o resyncfromreplica snapback snapshot
Caution: Always unmount the snapshot volume (if mounted) before performing
a snapback. In addition, you must unmount the file system corresponding to the
primary volume before using the resyncfromreplica option.
Adding plexes to a snapshot volume
If you want to retain the existing plexes in a snapshot volume after a snapback
operation, you can create additional snapshot plexes that are to be used for the
snapback.
To add plexes to a snapshot volume
1 Use the following
vxprint commands to discover the names of the snapshot
volume’s data change object (DCO) and DCO volume:
# DCONAME=‘vxprint [-g diskgroup] -F%dco_name snapshot‘
# DCOVOL=‘vxprint [-g diskgroup] -F%log_vol $DCONAME‘