Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

Preparing to create instant and break-off snapshots
To prepare a volume for the creation of instant and break-off snapshots
1
Use the following commands to see if the volume has a version 20 data change
object (DCO) and DCO volume that allow instant snapshots and Persistent
FastResync to be used with the volume, and to check that FastResync is
enabled on the volume:
# vxprint -g volumedg -F%instant volume
# vxprint -g volumedg -F%fastresync volume
If both commands return a value of on, skip to step 3. Otherwise continue
with step 2.
2
To prepare a volume for instant snapshots, use the following command:
# vxsnap [-g diskgroup] prepare volume [regionsize=size] \
[ndcomirs=number] [alloc=storage_attributes]
Run the vxsnap prepare command on a volume only if it does not have a
version 20 DCO volume (for example, if you have run the vxsnap unprepare
command on the volume).
See “Creating a volume with a version 20 DCO volume” on page 293.
See “Preparing a volume for DRL and instant snapshots” on page 318.
See “Removing support for DRL and instant snapshots from a volume”
on page 323.
For example, to prepare the volume, myvol, in the disk group, mydg, use the
following command:
# vxsnap -g mydg prepare myvol regionsize=128k ndcomirs=2 \
alloc=mydg10,mydg11
This example creates a DCO object and redundant DCO volume with two
plexes located on disks mydg10 and mydg11, and associates them with myvol.
The region size is also increased to 128KB from the default size of 64KB. The
region size must be a power of 2, and be greater than or equal to 16KB. A
smaller value requires more disk space for the change maps, but the finer
granularity provides faster resynchronization.
367Administering volume snapshots
Creating instant snapshots