HP StorageWorks XP Remote Web Console Software - Manual (Page 43)

and see the HP StorageWorks XP24000 Snapshot User’s Guide to calculate the number of differential
tables and pair tables that are required for XP Snapshot.
Assuming that only Business Copy uses differential tables and pair tables, this section describes how to
calculate the number of differential tables and pair tables required for one Business Copy pair, and the
conditions you need to consider when calculating the number of Business Copy pairs that can be created.
Note: You can use RAID Manager’s inqraid command to query the number of the differential tables
and pair tables required when you create Business Copy pairs. You can also query the number of the
differential tables and pair tables not used in the storage system by using this command. For details
about inqraid command, see the HP StorageWorks XP RAID Manager User’s Guide.
Calculation of the Number of Differential Tables and Pair Tables Required for One Pair
When you create a Business Copy pair, the number of required differential tables and pair tables will
change according to the emulation type of the volumes. To calculate the number of differential tables and
pair tables required for a pair according to the emulation type, use the expression in Table 9 on page 43.
Table 9 Total Number of Differential Tables Per Pair
Emulation Type Expression
OPEN-3, OPEN-8,
OPEN-9, OPEN-E,
OPEN-L
Total number of the differential tables per pair = ((X) ÷ 48 + (Y) Ч 15) ч (Z)
(X): The capacity of the volume. (KB)*
(Y): The number of the control cylinders. (See
Table 10 on page 44)
(Z): 20,448 (The number of the slots that can be managed by a differential
table)
Note that you should round up the number to the nearest whole number. For
example, if the emulation type of a volume is OPEN-3, and when provided that
the number of the cylinders of the divided volume is 2,403,360 KB ((X) in the
expression above), the calculation of the total number of the differential tables
is as follows.
(2,403,360 ч 48 + 8 Ч 15) ч 20,448 = 2.4545...
When you round up 2.4545 to the nearest whole number, it becomes 3.
Therefore, the total number of the differential tables for one pair is 3 when
emulation type is OPEN-3.
You may use 36 differential table per one pair table. The total number of the
pair tables is 1 when emulation type is OPEN-3.
OPEN-V
Total number of the differential tables per pair = ((X) ч 256) ч (Z)
(X): The capacity of the volume. (KB)
(Z): 20,448 (The number of the slots that can be managed by a differential
table)
Note that you should round up the number to the nearest whole number. For
example, if the emulation type of a volume is OPEN-V, and when provided that
the number of the cylinders of the divided volume is 3,019,898,880 KB ((X) in
the expression above), the calculation of the total number of the differential
tables is as follows.
(3,019,898,880 ч 256) ч 20,448 = 576.9014...
When you round up 576.9014 to the nearest whole number, it becomes 577.
Therefore, the total number of the differential tables for one pair is 577 when
emulation type is OPEN-V.
You may use 36 differential table per one pair table. The total number of the
pair tables is 17 when emulation type is OPEN-V. The emulation type of case
when multiple pair tables are used in the open system is only OPEN-V.
XP24000 Business Copy Software User's Guide 43