HP StorageWorks XP Remote Web Console Software - Manual (Page 21)

• XP Business Copy
• ShadowImage for z/OS
• Hitachi FlashCopy Mirroring
• Hitachi FlashCopy Mirroring Version 2
• Flex Copy XP
• Auto LUN XP
If you use any of these software products in the same array, calculate the number of differential tables
XP Snapshot pairs can use by subtracting the number of differential tables the pairs use (migration
plan for Auto LUN XP) for these software products from the number of differential tables for the whole
array.
For more information about calculating the number of required differential tables for XP Business
Copy, ShadowImage for z/OS, Hitachi FlashCopy Mirroring, Hitachi FlashCopy Mirroring Version
2, Flex Copy XP, and Auto LUN XP, see the software product's manual.
To calculate the number of differential tables for each XP Snapshot pair, use the following formula:
( (X) / 256) / (Z)
where:
(X) is the volume's capacity (in kilobytes)
(Z) is the number of slots a differential table can manage (1,916 x 32)
You must round up the calculation result to the nearest whole number.
If the volume's capacity ((X) in the previous formula) is 16 GB (16,777,216 KB), the number of
differential tables for each XP Snapshot pair is calculated as:
(16,777,216 / 256) / (1,916 x 32) = 1.06889
Round up 1.06889 to 2. Therefore, two differential tables are required to create a XP Snapshot pair.
Assume that no other software products use differential tables in an array where additional shared
memory is not installed. The number of differential tables that XP Snapshot can use is 13,652. To
create Snapshot pairs that require two differential tables for each pair, the calculation is as follows:
13,652 / 2 = 6,826
Therefore, you can create a maximum of 6,826 XP Snapshot pairs.
Using shared memory capacity for the virtual volume management area
The V-VOL management area consists of the following:
• Pool association information
• Pool management block
• Other management information (shared memory is fixed at 8 MB)
Table 5 on page 21 shows the shared memory capacity for the whole V-VOL management area.
Table 5 Shared Memory Capacity for the Whole V-VOL Management Area
Shared Memory Capacity for the Whole V-VOL Manage-
ment Area If a Shared Memory is Added to
536,870,912 bytes Basic
1,073,741,824 bytes Extension 1
XP Snapshot User Guide 21