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

319Administering volume snapshots
Creating instant snapshots
■ Dissociate the snapshot volume entirely from the original volume. This may be
useful if you want to use the copy for other purposes such as testing or report
generation. If desired, you can delete the dissociated volume. See “Dissociating
an instant snapshot” on page 330 for details.
■ If the snapshot is part of a snapshot hierarchy, you can also choose to split this
hierarchy from its parent volumes. See “Splitting an instant snapshot hierarchy”
on page 331 for details.
Creating and managing third-mirror break-off snapshots
Note: Break-off snapshots are suitable for write-intensive volumes, such as database redo
logs.
To turn one or more existing plexes in a volume into a break-off instant snapshot volume,
the volume must be a non-layered volume with a mirror or mirror-stripe layout,
or a RAID-5 volume that you have converted to a special layered volume (see “Using a
DCO and DCO volume with a RAID-5 volume” on page 269) and then mirrored. The
plexes in a volume with a stripe-mirror layout are mirrored at the subvolume level,
and cannot be broken off.
The attributes for a snapshot are specified as a tuple to the
vxsnap make command. This
command accepts multiple tuples. One tuple is required for each snapshot that is being
created. Each element of a tuple is separated from the next by a slash character (/). Tuples
are separated by white space.
To create and manage a third-mirror break-off snapshot
1 To create the snapshot, you can either take some of the existing ACTIVE plexes in
the volume, or you can use the following command to add new snapshot mirrors to
the volume:
# vxsnap [-b] [-g diskgroup] addmir volume [nmirror=N] \
[alloc=storage_attributes]
By default, the vxsnap addmir command adds one snapshot mirror to a volume
unless you use the nmirror attribute to specify a different number of mirrors. The
mirrors remain in the SNAPATT state until they are fully synchronized. The
-b
option can be used to perform the synchronization in the background. Once
synchronized, the mirrors are placed in the SNAPDONE state.
For example, the following command adds 2 mirrors to the volume, vol1, on disks
mydg10 and mydg11:
# vxsnap -g mydg addmir vol1 nmirror=2 alloc=mydg10,mydg11