Veritas FlashSnap Point-In-Time Copy Solutions 5.0.1 Administrators Guide, HP-UX 11i v3, First Edition, November 2009

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=no \

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

init=active [storage_attributes]

It is recommended that you specify the same number of DCO mirrors

(ndcomirror) as the number of mirrors in the volume (nmirror). The

init=active attribute is used to make 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 a shared cache object

If you need to create several instant space-optimized snapshots for the volumes

in a disk group, you may find it more convenient to create a single shared cache

object in the disk group rather than a separate cache object for each snapshot.

To create a shared cache object

Decide on the following characteristics that you want to allocate to the cache

volume that underlies the cache object:

■ The size of the cache volume should be sufficient to record changes to the

parent volumes during the interval between snapshot refreshes. A

suggested value is 10% of the total size of the parent volumes for a refresh

interval of 24 hours.

Setting up volumes for instant snapshots

Creating a shared cache object