HP StorageWorks XP Remote Web Console Software - Manual (Page 26)

S1 = S – S2 - 8
S — Shared memory capacity for the whole V-VOL management area (in bytes)
S2 — Shared memory capacity for pool management block (in bytes)
8 — Fixed management information (in megabytes).
NOTE:
You can check the capacity of the shared memory of pool association information and pool management
block in the Snapshot XP pane.
To calculate S2 (Shared memory capacity for pool management block), use the formula below:
S2 = ↑{( Y ч 256) Ч (32 ч 74784)}↑ Ч 74784
Y — Total capacity of the pool-VOLs (in kilobytes) 256: Capacity of one slot (in kilobytes)
32 — Capacity of the table which you need to manage the pool of one slot 74784: Minimum size
of pool management block.
NOTE:
You must round up the value enclosed by two upward arrows (↑) to the nearest whole number.
NOTE:
•
You can check the shared memory capacity of the pool association information and pool
management block in the Snapshot XP pane ( Figure 18 ).
NOTE:
When calculating a pool's usage:
• When copying snapshot data to the pool, Snapshot XP always uses a multiple of 256 KB of the pool's
capacity, even when the snapshot data is smaller than 256 KB.
• When snapshot data is stored consecutively, snapshot data capacity and pool usage is almost the
same. However, pool usage will be larger than snapshot data capacity when snapshot data is
stored randomly.
When the shared memory capacity for the whole V-VOL management area (“S” in the formula above) is
1,024 MB, the capacity of the pool-VOL (“Y” in the formula above) is 4 TB (4,398,046,511,104 kB),
and the capacity of one P-VOL is 10 GB, the number of Snapshot XP pairs that can be created for a
subsystem can be calculated as follows.
26 Requirements for Snapshot XP operations