HP XP20000 User Manual download pdf (Page 38)

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 “XP Snapshot Window” (page 53).

For the capacity of the shared memory for the whole V-VOL management area, see “Additional

Shared Memory for the V-VOL Management Area” (page 37).

To calculate S2 (shared memory capacity for pool management block), use the following formula:

S2 = [{(P ÷ 256) × 32} ÷ 8,736] × 8,736 + [{(Y ÷ 256) ÷ 270} ÷

2,048] × 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 ÷ 256) × 32} ÷ 8,736 × 8,736 +

[{( 4,282,451,296 ÷ 256) ÷ 270} ÷ 2,048 ] × 8,736

=↑61,275.917... × 8,736 + 30.252...↑ × 8,736

= 61,276 × 8,736 + 31 × 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 ÷ 8,736) × 2,048 × 256

= ↑60,402.714... × 2,048 × 256

= 60,403 × 2,048 × 256

= 31,668,568,064

Maximum number of XP Snapshot pairs =

Maximum number of XP Snapshot pairs

= 31,668,568,064 ÷

38 Preparing for XP Snapshot Operations

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HP XP20000 User Manual Page 38

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