HP StorageWorks 2000 Series Reference Manual page 112

Halt Writes – Halts all writes to the master volume (each write returns an error).
Snapshot data is preserved.
Delete Oldest Snapshots – Deletes the oldest snapshots until the amount of data
in the snap pool is below the threshold.
7. Click Set Policy & Threshold.
The changes take effect immediately.
You can take snapshots of a snapshot-enabled volume (a master volume). A
maximum of 16 master volumes can exist and they all can be associated with a
single snap pool. A master volume and its snap pool can be in different virtual
disks, but must be owned by the same controller.
You can either:
Create a master volume, as described below
Convert a standard volume to a master volume; see "Converting a Standard
Volume to a Master Volume" on page 113
To create a master volume:
1. Select Manage > Volume Management > Snapshot Services > Create Master
Volume.
For each virtual disk, the virtual disk panel shows a status icon; the name, RAID
level, size, number of disk drives, and number of volumes; and utility status, if any.
2. Select the virtual disk where you want to create the volume.
The selected virtual disk's volume names, sizes, and types are displayed, and the
amount of free space.
3. Select a snap pool.
Only snap pools owned by the same controller as the selected virtual disk are listed.
4. Type a size in increments of 1 Mbyte for the new volume.