HP StorageWorks XP Remote Web Console Software - Manual (Page 37)

S2 = [{(P ч 256) Ч 32} ч 8,736] Ч 8,736 + [{(Y ч 256) ч 270} ч
2,048] Ч 8,736
P: Total capacity of all pools (in kilobytes)
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
8,736: Minimum size of the pool management block (in bytes)
270: Number of slots that can be managed by the slot management table
2,048: Number of slots that can be managed by the pool management block of the minimum size
Note that you must round up the value enclosed by the two upward arrows (
↑) to the nearest whole
number.
To calculate P (total capacity of all pools), use the following formula:
P = Y – (4,116,000 + 84,000 × Number of pool-VOLs)
Following are notes on calculating the usage of a pool:
•
When copying snapshot data to the pool, XP Snapshot always consumes a multiple of 256
kB of the capacity of the pool. 256 kB will be consumed even if the snapshot data is smaller
than 256 kB.
•
When snapshot data is stored consecutively, the capacity of the snapshot data and the usage
of the pool will be almost the same. However, the usage of the pool will be larger than the
capacity of the snapshot data in some cases, when snapshot data is stored randomly.
When the shared memory capacity for the whole V-VOL management area (S in the previous
formula) is 1,024 MB, the capacity of the pool-VOL (Y in the previous formula) is 4 TB
(4,294,967,296 kB), the number of the pool-VOLs is 100, and the capacity of one P-VOL is 10
GB, the number of XP Snapshot pairs that can be created for a subsystem can be calculated as
follows.
Example
P = 4,294,967,296 (4,116,000 + 84,000 × 100)
= 4,282,451,296
S2 = [{( 4,282,451,296 ч 256) Ч 32} ч 8,736 Ч 8,736 +
[{( 4,282,451,296 ч 256) ч 270} ч 2,048 ] Ч 8,736
=
↑61,275.917... Ч 8,736 + 30.252...↑ Ч 8,736
= 61,276 Ч 8,736 + 31 Ч 8,736
= 535,577,952
S1 = 1,073,741,824 – 535,577,952 –10,485,760
= 527,678,112
Total capacity of P-VOLs (kB) = ( 527,678,112 ч 8,736) Ч 2,048 Ч 256
=
↑60,402.714... Ч 2,048 Ч 256
= 60,403 Ч 2,048 Ч 256
= 31,668,568,064
Maximum number of XP Snapshot pairs =
Maximum number of XP Snapshot pairs
= 31,668,568,064 ч
[ {(10 Ч 1,024 Ч 1,024) ч 524,288} Ч 524,288]
= 31,668,568,064 ч 10,485,760
= 3,020
According to the result, the maximum number of XP Snapshot pairs that can be created is 3,020.
If shared memory is added to your storage system and you know the pool capacity, you can
roughly estimate the capacity of a P-VOL that can be created, see
Table 19 (page 38) . To calculate
the actual capacity of a P-VOL that can be created, use the above formulas.
Operational Requirements 37