HP StorageWorks Snapshot XP user guide (T1713-96023, October 2006)

S1=S–S2-8

S — Shared memor

y capacity for the whole V-VOL management area (in bytes)

S2 — Shared memo

ry capacity for pool management block (in bytes)

8 — Fixed manage

ment information (in megabytes).

NOTE:

You can check the capacity of the share d memory of pool associatio n information and pool management

block in the Snapshot XP pane.

To calculate S 2 (Shared memor y capacity for pool management block) , use the formula below:

S2 = ↑{( Y ÷ 256) × (32 ÷ 74784)}↑ ×74784

Y — Total capacity of the pool-VOLs (in kilobytes) 2 56: 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 p ool association inform ation 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

capacit y, even when the snapshot data is smaller than 256 KB.

• When snapshot data is stored consecuti vely, 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 sha

red memory capacity for the whole V-VOL management a rea ( “S” in the formula above) is

1,024 MB, t

he 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 pa irs that can be created for a

subsystem can be calculated as follows.

Requirements for Snapshot XP operations