HP Veritas Volume Manager 5.0 -UX 11i v3 manual For example to start the cache object, cobjmydg

Administering volume snapshots

Creating instant snapshots

323

Note: All space-optimized snapshots that share the cache must have a region size that is equal to or an integer multiple of the region size set on the cache. Snapshot creation also fails if the original volume’s region size is smaller than the cache’s region size.

If the region size of a space-optimized snapshot differs from the region size of the cache, this can degrade the system’s performance compared to the case where the region sizes are the same.

If the cache is to be allowed to grow in size as required, specify autogrow=on. By default, the ability to automatically grow the cache is turned off.

In the following example, the cache object, cobjmydg, is created over the cache volume, cachevol, the region size of the cache is set to 32KB, and the autogrow feature is enabled:

#vxmake -g mydg cache cobjmydg cachevolname=cachevol \ regionsize=32k autogrow=on

4Having created the cache object, use the following command to enable it:

#vxcache [-gdiskgroup] start cache_object

For example to start the cache object, cobjmydg:

#vxcache -g mydg start cobjmydg

For details of how to remove a cache, see “Removing a cache” on page 347.

Creating a volume for use as a full-sized instant or linked break-off snapshot

To create an empty volume for use by a full-sized instant snapshot or a linked break-off snapshot

1Use the vxprint command on the original volume to find the required size for the snapshot volume.

#LEN=‘vxprint [-g diskgroup] -F%len volume‘

Note: The command shown in this and subsequent steps assumes that you are using a Bourne-type shell such as sh, ksh or bash. You may need to modify the command for other shells such as csh or tcsh.

2Use the vxprint command on the original volume to discover the name of its DCO:

#DCONAME=‘vxprint [-g diskgroup] -F%dco_name volume‘

3Use the vxprint command on the DCO to discover its region size (in blocks):

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