HP XP RAID Manager Software - Manual (Page 15)

Calculating maximum pairs based on V-VOL management area shared memory
This section helps you calculate the number of pairs allowed based on the amount of additional
shared memory in the V-VOL management area.
The V-VOL management area consists of the following:
•
Pool association information
•
Pool management block
Shared memory capacity for the V-VOL management area depends on additional shared memory.
The following table shows the shared memory capacity of a system based on the amount of
additional shared memory.
Table 3 Shared Memory Capacity for V-VOL Management Area
Shared Memory Capacity Shared Memory
751,619,276 bytes Snapshot
4,294,967,296 bytes Snapshot Extension 1
Using the shared memory capacity of your V-VOL management area, you can calculate the maximum
number of pairs. This is done by performing the following calculations in the order presented. The
result of each calculation is used in the next calculation.
1.
Total capacity of all pools (P)
2. Shared memory capacity of the pool management block (S2)
3. Shared memory capacity of pool association information (S1)
4. Total capacity of P-VOLs
5. Maximum number of Snapshot pairs
NOTE: "ceil" indicates that the result within the parenthesis () that follows must be rounded up.
1. Calculate total capacity of all pools (P), using the following formula:
P = Y – (4,116,000 + 84,000 × Number of pool-VOLs)
where Y = total capacity of pool-VOLs (in kilobytes).
For example:
This example assumes that Y is 4 TB (4,294,967,296 kB) and the number of pool-VOLs is 100.
P = 4,294,967,296 - (4,116,000 + 84,000 × 100)
= 4,282,451,296
NOTE: When copying Snapshot data to the pool, pool capacity is used in multiples of 256 KB,
even though Snapshot data may be smaller than 256 kB. When Snapshot data is stored
consecutively, the actual size and usage of pool capacity may be nearly the same. But when
Snapshot data is stored randomly, the pool capacity used is larger than the data's actual size.
2. Calculate shared memory capacity for the pool management block (S2), using the following
formula:
S2 = ceil[{(Y ч 256) Ч 32} ч 8,640] Ч 8,736 + ceil[Y ч 2,097,152] Ч 8,736
where:
Y = Total capacity of the pool-VOLs (in kilobytes)
256 = Capacity of one slot (in kilobytes)
32 = Capacity of the table that you need to manage the pool of one slot
8,736 = Minimum size of pool management block (in bytes)
8,640 = Data size of pool management block (in bytes)
Number of pairs 15