APC RAID Subsystem SCSI-SATA II - Manual (Page 75)

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These numbers mean “Free snapshot space” and “Total snapshot
space”.
4. Choose a UDV by clicking the checkbox of the row and then click
“ ”.
5. A snapshot UDV is created with the date and time taken snapshot of
the chosen UDV. The snapshot UDV size is the same as the chosen
UDV no matter the actual snapshot UDV data occupies.
6. Attach LUN to UDV, please refer to section 3.6.6 Logical unit number
for more detail.
7. Done. It can be used as a disk.
Figure 4.4.1.1
(Figure 4.4.1.1: No.1 is a RAID 0 UDV. Set snapshot space to 10GB. And now its space is
free to snapshot. No.2 is a snap UDV taken on 02/14 17:13:35.)
Snapshot has some constraints as the following:
1. Minimum RAM size of enabling snapshot function is 512MB.
2. For performance concern and future rollback, the system saves
snapshot with names in sequences. For example: three snapshots has
been taken and named “snap1”(first), “snap2” and “snap3”(last). When
deleting “snap2”, both of “snap1” and “snap2” will be deleted because
“snap1” are related to “snap2”.
3. For resource concern, the max number of snapshots is 32.
4. If snapshot space is full, controller will send a warning message about
space full and the new taken snapshot will replace the oldest snapshot
by rotation sequence.
5. Snap UDV cannot be migrated, when doing migration of related VG,
snap UDV will fail.
6. Snap UDV cannot be extended.