Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Creating Instant Snapshots
284 VERITAS Volume Manager Administrator’s Guide
In this example, sequential DRL is enabled for the snapshots of the redo log volumes, and
normal DRL is applied to the snapshots of the volumes that contain the database tables.
The two space-optimized snapshots are configured to share the same cache object in the
disk group. Also note that break-off snapshots are used for the redo logs as such volumes
are write intensive.
Creating Instant Snapshots of Volume Sets
Volume set names can be used in place of volume names with the following vxsnap
operations on instant snapshots: addmir, dis, make, prepare, reattach, refresh,
restore, rmmir, split, syncpause, syncresume, syncstart, syncstop,
syncwait, and unprepare.
The procedure for creating an instant snapshot of a volume set is the same as that for a
standalone volume. However, there are certain restrictions if a full-sized instant snapshot
is to be created from a prepared volume set. A full-sized instant snapshot of a volume set
must itself be a volume set with the same number of volumes, and the same volume sizes
and index numbers as the parent. For example, if a volume set contains three volumes
with sizes 1GB, 2GB and 3GB, and indexes 0, 1 and 2 respectively, then the snapshot
volume set must have three volumes with the same sizes matched to the same set of index
numbers. The corresponding volumes in the parent and snapshot volume sets are also
subject to the same restrictions as apply between standalone volumes and their snapshots.
You can use the vxvset list command to verify that the volume sets have identical
characteristics as shown in this example:
# vxvset -g mydg list vset1
VOLUME INDEX LENGTH KSTATE CONTEXT
vol_0 0 204800 ENABLED -
vol_1 1 409600 ENABLED -
vol_2 2 614400 ENABLED -
# vxvset -g mydg list snapvset1
VOLUME INDEX LENGTH KSTATE CONTEXT
svol_0 0 204800 ENABLED -
svol_1 1 409600 ENABLED -
svol_2 2 614400 ENABLED -
A full-sized instant snapshot of a volume set can be created using a prepared volume set
in which each volume is the same size as the corresponding volume in the parent volume
set. Alternatively, you can use the nmirrors attribute to specify the number of plexes
that are to be broken off provided that sufficient plexes exist for each volume in the
volume set.