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

342 Administering volume snapshots
Creating traditional third-mirror break-off snapshots
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‘
2Use the vxassist mirror command to create mirrors of the existing snapshot
volume and its DCO volume:
# vxassist -g diskgroup mirror snapshot
# vxassist -g diskgroup mirror $DCOVOL
Note: The new plex in the DCO volume is required for use with the new data plex in
the snapshot.
3Use the
vxprint command to find out the name of the additional snapshot plex:
# vxprint -g diskgroup snapshot
4Use the vxprint command to find out the record ID of the additional DCO plex:
# vxprint -g diskgroup -F%rid $DCOVOL
5Use the vxedit command to set the dco_plex_rid field of the new data plex to
the name of the new DCO plex:
# vxedit -g diskgroup set dco_plex_rid=dco_plex_rid new_plex
The new data plex is now ready to be used to perform a snapback operation.