HP StorageWorks XP Remote Web Console Software - Manual (Page 25)

( (X) ч 256) ч (Z)
where:
(X) is the volume's capacity (in kilobytes)
(Z) is the number of slots a differential table can manage (1,916 × 32)
You must round up the calculation result to the nearest whole number.
If the volume's capacity ((X) in the previous formula) is 16 GB (16,777,216 KB), the number of differential
tables for each Snapshot XP pair is calculated as:
(16,777,216 ч 256) ч (1,916 Ч 32) = 1.06889
Round up 1.06889 to 2. Therefore, two differential tables are required to create a Snapshot XP pair.
Assume that no other software products use differential tables in an array where additional shared
memory is not installed. The number of differential tables that Snapshot XP can use is 13,652. To create
Snapshot pairs that require two differential tables for each pair, the calculation is as follows:
13,652 ÷ 2 = 6,826
Therefore, you can create a maximum of 6,826 Snapshot XP pairs.
Using shared memory capacity for the virtual volume management area
The V-VOL management area consists of the following:
• Pool association information
• Pool management block
• Other management information (shared memory is fixed at 8 MB)
To calculate the maximum number of Snapshot XP pairs you can create for an array, use the following
formula:
Maximum number of Snapshot XP pairs = Total capacity of P-VOLs ÷ { ↑(Capacity of one P-VOL ч 4)↑Ч4}
4 — Unit by which pool association information manage the capacity of a P-VOL (in gigabytes).
NOTE:
You must round up the value enclosed by two upward arrows (↑) to the nearest whole number.
NOTE:
Pool association information manages the P-VOL capacity by 4 GB. For example, if the capacity of a
P-VOL is 10 GB, pool association information capacity will be 12 GB, not 10 GB.
To calculate the total capacity of P-VOLs, use the formula below:
Total capacity of P-VOLs = ↑(S1 ч 74784)↑ Ч 16384 Ч 256
S1 — Shared memory capacity for pool association information (in bytes) 74784: Capacity of pool
association information per one table (in bytes) 16384: Number of slots of P-VOL which can be managed
by the pool association information of one table 256: Capacity of one slot (in kilobytes).
NOTE:
You must round up the value enclosed by two upward arrows (↑) to the nearest whole number.
To calculate S1 (Shared memory capacity for pool association information), use the formula below:
HP StorageWorks Snapshot XP user guide 25