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

328 Administering volume snapshots
Creating instant snapshots
Note: The snapshot being reattached must not be open to any application. For example,
any file system configured on the snapshot volume must first be unmounted.
It is possible to reattach a volume to an unrelated volume provided that their volume sizes
and region sizes are compatible.
For example the following command reattaches one plex from the snapshot volume,
snapmyvol, to the volume, myvol:
# vxsnap -g mydg reattach snapmyvol source=myvol nmirror=1
While the reattached plexes are being resynchronized from the data in the parent volume,
they remain in the SNAPTMP state. After resynchronization is complete, the plexes are
placed in the SNAPDONE state. You can use the
vxsnap snapwait command (but not
vxsnap syncwait) to wait for the resynchronization of the reattached plexes to complete,
as shown here:
# vxsnap -g mydg snapwait myvol nmirror=1
Note: If the volume and its snapshot have both been resized (to an identical smaller or
larger size) before performing the reattachment, a fast resynchronization can still be
performed. A full resynchronization is not required. Version 20 DCO volumes are resized
proportionately when the associated data volume is resized. For version 0 DCO volumes,
the FastResync maps stay the same size, but the region size is recalculated, and the
locations of the dirty bits in the existing maps are adjusted. In both cases, new regions are
marked as dirty in the maps.
Reattaching a linked break-off snapshot volume
Unlike other types of snapshot, the reattachment operation for linked break-off snapshot
volumes does not return the plexes of the snapshot volume to the parent volume. The link
relationship is re-established that makes the snapshot volume a mirror of the parent
volume, and this allows the snapshot data to be resynchronized. However, the snapshot
volume is only readopted by its parent volume if they are both in the same disk group.
To reattach a linked break-off snapshot volume, use the following form of the
vxsnap
reattach command:
# vxsnap [-g snapdiskgroup] reattach snapvolume|snapvolume_set \
source=volume|volume_set [sourcedg=diskgroup]
The sourcedg attribute must be used to specify the data volume’s disk group if this is
different from the snapshot volume’s disk group, snapdiskgroup.