HP StorageWorks XP Remote Web Console Software - Manual (Page 19)

Snapshot XP user guide 19
• After you install additional shared memory for the V-VOL management area, you cannot partially
uninstall it. To uninstall additional shared memory for the V-VOL management area, you must uninstall
the entire shared memory that was added for the V-VOL management area.
• Skip step 1 if shared memory for the differential tables is already installed.
• Note that step 2 and step 3 are interchangeable.
• Skip step 3 if Business Copy XP is already installed on the disk array.
Calculating the number of Snapshot XP pairs that can be created
The number of Snapshot XP pairs you can create for a disk array depends on the number of differential
tables, V-VOL management area’s shared memory capacity, or number of pair tables. To calculate the
number of Snapshot XP pairs that can be created, first use the number of differential tables, then use the
V-VOL management area’s shared memory capacity, and finally use the number of pair tables. Then
compare the three results. The smallest value is the maximum number of Snapshot XP pairs you can create
for the disk array.
Using the number of differential tables
A maximum of 13,652 differential tables can be used for a disk array if additional shared memory is not
installed. A maximum of 30,718 differential tables can be used if additional shared memory is installed.
To calculate the number of Snapshot XP pairs that can be created, calculate the number of differential
tables required for the Snapshot XP pair and compare it with the number of differential tables for the whole
disk array. In addition to Snapshot XP, the following software products use differential tables in the
XP10000/XP12000:
• Business Copy XP
• ShadowImage for z/OS
• Hitachi FlashCopy Mirroring
• Hitachi FlashCopy Mirroring Version 2
• Flex Copy XP
• Auto LUN XP
If any of these software products are used in the same disk array, calculate the number of differential tables
Snapshot XP 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 disk array.
For more information about calculating the number of required differential tables for Business Copy XP,
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 Snapshot XP pair, use the following formula:
( (X) ч 256) ч (Z)
where:
(X) is the volume’s capacity (in kilobytes)
(Z) is the number of slots a differential table can manage (1,916 × 32)
Note that 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 (16,777,214 KB), the number of differential
tables for each Snapshot XP pair is calculated as:
(16,777,214 ч 256) ч (1,916 Ч 32) = 1.06889
Round up 1.06889 to 2. Therefore, two differential tables are required to create a Snapshot XP pair.
Assume that no other software products use differential tables in a disk array where additional shared
memory is not installed. The number of differential tables that Snapshot XP can use is 13,652. To create
Snapshot pairs that require two differential tables for each pair, the calculation is as follows:
13,652 ч 2 = 6,826