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330 Administering volume snapshots
Creating instant snapshots
If you specify the -b option to the vxsnap addmir command, you can use the
vxsnap snapwait command to wait for synchronization of the snapshot
plexes to complete, as shown in this example:
# vxsnap -g mydg snapwait vol1 nmirror=2
2 To create a third-mirror break-off snapshot, use the following form of the
vxsnap make command.
# vxsnap [-g diskgroup] make source=volume[/newvol=snapvol]\
{/plex=plex1[,plex2,...]|/nmirror=number]}
Either of the following attributes may be specified to create the new
snapshot volume, snapvol, by breaking off one or more existing plexes in
the original volume:
plex Specifies the plexes in the existing volume that are to be broken
off. This attribute can only be used with plexes that are in the
ACTIVE state.
nmirror Specifies how many plexes are to be broken off. This attribute
can only be used with plexes that are in the SNAPDONE state.
(Such plexes could have been added to the volume by using the
vxsnap addmir command.)
Snapshots that are created from one or more ACTIVE or SNAPDONE plexes
in the volume are already synchronized by definition.
For backup purposes, a snapshot volume with one plex should be sufficient.
For example, to create the instant snapshot volume, snap2myvol, of the
volume, myvol, in the disk group, mydg, from a single existing plex in the
volume, use the following command:
# vxsnap -g mydg make source=myvol/newvol=snap2myvol\
/nmirror=1
The next example shows how to create a mirrored snapshot from two
existing plexes in the volume:
# vxsnap -g mydg make source=myvol/newvol=snap2myvol\
/plex=myvol-03,myvol-04
3 Use fsck (or some utility appropriate for the application running on the
volume) to clean the temporary volume’s contents. For example, you can use
this command with a VxFS file system:
# fsck -F vxfs /dev/vx/rdsk/diskgroup/snapshot
4 If you require a backup of the data in the snapshot, use an appropriate
utility or operating system command to copy the contents of the snapshot to
tape, or to some other backup medium.
5 You now have the following choices of what to do with a third-mirror break-
off snapshot:
■ Refresh the contents of the snapshot. This creates a new point-in-time
image of the original volume ready for another backup. If