HP XP Racks - Manual (Page 23)

3. Calculate the maximum number of pairs, which is restricted by the following:
•
The number of bitmap areas required for Continuous Access Synchronous (calculated
above).
•
The total number of bitmap areas in the storage system, which is 65,536.
Bitmap areas are also used by Continuous Access Synchronous Z, Continuous Access
Journal, and Continuous Access Journal Z.
Therefore, the number of bitmap areas used by these other program products (if any)
must be subtracted from 65,536, with the difference used to calculate the maximum
number of pairs for Continuous Access Synchronous.
If Continuous Access Synchronous and Continuous Access Journal share the same volume,
you must use the total number of bitmap areas for both pairs regardless of whether the
shared volume is local or remote.
•
The maximum number of pairs supported per storage system, which is 65,280 (65,279
if RAID Manager is used).
Use the following formula:
Maximum number of pairs = floor (Total number of bitmap areas in
the storage system / Required number of bitmap areas)
If the calculated maximum number of pairs exceeds the total number of LDEVs of the storage
system, and the total number of LDEVs of the storage system is less than 65,280, then the total
number of LDEVs of the storage system becomes the maximum number of pairs.
Priority for initial copy operations and scheduling order
Though you can specify a maximum number of initial copies to run concurrently, you are allowed
to perform more initial copies than this when creating pairs. If you do this, you will set the scheduling
order for the additional operations in the Priority field when creating the pair.
This topic provides two examples in which priority and the pre-set scheduling order are discussed.
Example 1: more initial copies than previously specified
In this example, four initial copies are being created in the same operation, but Maximum Initial
Copy Activities is set at 2. In this scenario, the Priority field in the Create Pairs window would be
set as shown in the following table.
Value set for Priority P-VOL
2 LUN 00
3 LUN 01
1 LUN 02
4 LUN 03
The order for the initial copy and the Priority for the P-VOLs are shown in the following table.
Value set for Priority P-VOL Order for initial copy
1 LUN 02 1
2 LUN 00 2
3 LUN 01 3
4 LUN 03 4
Planning pairs and pair volumes 23