HP StorageWorks XP Remote Web Console Software User Manual
Page 20
20
Snapshot XP
Therefore, a maximum of 6,826 Snapshot XP pairs can be created.
Using shared memory capacity for the virtual volume management area
The V-VOL management area consists of the following elements:
•
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 that can be created for a disk array, use the
following formula:
{ ( (X) - 8)
÷
( (
α
) + (
β
) ) }
where:
(X) is shared memory capacity for the whole V-VOL management area (in megabytes)
(
α
) is shared memory capacity for the pool association information (in bytes)
(
β
) is shared memory capacity for the pool management block (in bytes)
Note that you should round off the calculation result to the nearest whole number.
The following is the calculation of the shared memory capacity of the pool association information (
α
) and
the shared memory capacity of the pool management block (
β
):
NOTE:
•
You can check the shared memory capacity of the pool association information and pool management
block in the Snapshot XP pane (see
•
If all the V-VOL management area’s capacity is used by the pool management block and pool
association information, the capacity ratio of the pool management block and pool association
information in the V-VOL management area is fixed. For more information, see ”
(
α
) =
↑
( (Y) ч 256)
↑ Ч
4
Ч
1.08
(
β
) =
↑
( (Z) ч 256)
↑ Ч
32
where:
(Y) is pool-VOL’s capacity (in kilobytes)
(Z) is pool usage (in kilobytes)
Note that you must round up the value enclosed by two upward arrows (
↑
) to the nearest whole number.
NOTE:
When calculating a pool’s usage:
•
When copying snapshot data to the pool, Snapshot XP always uses a multiple of 256 KB of the pool’s
capacity, even when the snapshot data is smaller than 256 KB.
•
When snapshot data is stored consecutively, snapshot data capacity and pool usage is almost the
same. However, pool usage might be larger than snapshot data capacity when snapshot data is
randomly stored.
When shared memory capacity for the whole V-VOL management area ((X) in the previous formula) is
2,047 MB, pool-VOL capacity ((Y) in the previous formula) is 16 GB (16,777,214 KB), and pool usage ((Z)
in the previous formula) is 1 GB (1,048,576 KB), the number of Snapshot XP pairs that can be created for
a disk array is calculated as:
(2047 - 8)
ч
[ { (16,777,214
ч
256)
Ч
4
Ч
1.08} + { (1,048,576
ч
256)
Ч
32} ] = 5162.02933...
According to these results, a maximum of 5,162 Snapshot XP pairs can be created.