HP StorageWorks XP Remote Web Console Software - Manual (Page 36)

Calculating the Number of XP Snapshot Pairs by Using the Shared Memory Capacity for the Virtual
Volume Management Area
The V-VOL management area consists of the following three elements:
•
Pool association information
•
Pool management block
•
Management information other than those above (shared memory is fixed to 10 MB)
The shared memory of the V-VOL management area differs according to the additional shared
memory.
Table 18 (page 36) shows the detailed information.
Table 18 Additional Shared Memory for the V-VOL Management Area
Shared Memory Capacity Shared Memory
751,619,276 bytes XP Snapshot 1
1,073,741,823 bytes XP Snapshot 2
2,147,483,647 bytes XP Snapshot 3
3,221,159,935 bytes XP Snapshot 4
4,294,901,759 bytes XP Snapshot 5
To calculate the maximum number of XP Snapshot pairs that can be created for a subsystem, use
the following formula:
Maximum number of XP Snapshot pairs = Total capacity of P-VOLs ÷
{ (Capacity of one P-VOL ч 524,288) Ч 524,288}
524,288: Unit by which pool association information manages the capacity of a P-VOL (in kilobytes)
You must round up the value enclosed by the two upward arrows (
↑) to the nearest whole number.
NOTE: Pool association information manages the P-VOL capacity by 524,288 KB.
To calculate the total capacity of P-VOLs, use the following formula:
Total capacity of P-VOLs = (S1 ч 8,736) Ч 2,048 Ч 256
S1: Shared memory capacity for pool association information (in bytes)
8,736: Capacity of pool association information per one table (in bytes)
2,048: Number of slots of the P-VOL which can be managed by the pool association information
for one table
256: Capacity of one slot (in kilobytes)
Note that you must round up the value enclosed by the two upward arrows (
↑) to the nearest whole
number.
To calculate S1 (shared memory capacity for pool association information), use the following
formula:
S1 = S − S2 - 10,485,760
S: Shared memory capacity for the whole V-VOL management area (in bytes)
S2: Shared memory capacity for the pool management block (in bytes)
10,485,760: Fixed management information (in bytes)
NOTE: You can check the capacity of the shared memory of the pool association information
and the pool management block in the XP Snapshot window. See (page 51) .
For the capacity of the shared memory for the whole V-VOL management area, see (page 36) .
To calculate S2 (shared memory capacity for pool management block), use the following formula:
36 Preparing for XP Snapshot Operations