HP Veritas Volume Manager 5.0 -UX 11i v3 Creating and managing space-optimized instant snapshots

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Administering volume snapshots

Creating instant snapshots

4Use 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]

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 and managing space-optimized instant snapshots

Note: 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 the performance of the volume.

If you intend 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 for this purpose.

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.

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.