Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)

Use the vxprint command on the DCO to discover its region size (in blocks):

# RSZ=`vxprint [-g diskgroup] -F%regionsz $DCONAME`

Use the vxassist command to create a volume, snapvol, of the required size

and redundancy, together with a version 20 DCO volume with the correct

region size:

# vxassist [-g diskgroup] make snapvol $LEN \

[layout=mirror nmirror=number] logtype=dco drl=off \

dcoversion=20 [ndcomirror=number] regionsz=$RSZ \

init=active [storage_attributes]

Storage attributes give you control over the devices, including disks and

controllers, which vxassist uses to configure a volume.

Specify the same number of DCO mirrors (ndcomirror) as the number of

mirrors in the volume (nmirror). The init=active attribute makes the volume

available immediately. You can use storage attributes to specify which disks

should be used for the volume.

As an alternative to creating the snapshot volume and its DCO volume in a

single step, you can first create the volume, and then prepare it for instant

snapshot operations as shown here:

# vxassist [-g diskgroup] make snapvol $LEN \

[layout=mirror nmirror=number] init=active \

[storage_attributes]

# vxsnap [-g diskgroup] prepare snapvol [ndcomirs=number] \

regionsize=$RSZ [storage_attributes]

Creating and managing space-optimized instant snapshots

Space-optimized instant snapshots are not suitable for write-intensive volumes

(such as for database redo logs) because the copy-on-write mechanism may degrade

performance.

To split the volume and snapshot into separate disk groups (for example, to

perform off-host processing), you must use a fully synchronized full-sized instant,

third-mirror break-off or linked break-off snapshot (which do not require a cache

object). You cannot use a space-optimized instant snapshot.

Creation of space-optimized snapshots that use a shared cache fails if the region

size specified for the volume is smaller than the region size set on the cache.

Administering volume snapshots

Creating instant snapshots

218