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

Snapshot User Guide to calculate the number of differential tables and pair tables that are required
for XP Snapshot.
Assuming that only XP 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 XP Business
Copy pair, and the conditions you need to consider when calculating the number of XP Business
Copy pairs that can be created.
You can use RAID Manager’s inqraid command to query the number of the differential tables and
pair tables required when you create XP 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 XP RAID Manager User Guide.
Calculation of the Number of Differential Tables and Pair Tables Required for One Pair
When you create an XP 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 shown in
Table 16 (page 43) .
Table 16 Total Number of Differential Tables Per Pair
Expression Emulation Type
Total number of the differential tables per pair = ((X) 48 + (Y) x 15) (Z)
(X): The capacity of the volume. (KB)*
OPEN-3, OPEN-8, OPEN-9,
OPEN-E, OPEN-L
(Y): The number of the control cylinders. (See Table 17 (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 48 + 8 x 15) 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.
Total number of the differential tables per pair = ((X) 256) (Z) OPEN-V
(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:
(3,019,898,880 256) 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.
If the volume is divided by VLL function, you need to apply the capacity of the volume after the
division. You cannot perform VLL operations on an OPEN-L volume. Therefore, if the emulation
type is OPEN-L, the value substitute for (X) is the default capacity of the volume.
Table 17 (page 44) lists the number of the control cylinders according to the emulation types.
Assessing Requirements 43