HP XP P9500 Storage - Manual (Page 14)

Planning number of pairs
This section provides instructions for calculating the number of system resources required for one
Business Copy pair. With this information you can calculate the maximum number of pairs allowed
on your system.
When you create pairs, differential tables (tables managing differential bitmaps) and pair tables
are required. These must be available in sufficient number to handle all the pairs you will create.
The number of differential and pair tables that are present in the system depends on additional
shared memory that is installed. Therefore, you must insure that you have sufficient additional
shared memory to handle the number of pairs.
The following table shows the number of differential and pair tables and the number of volumes
allowed per additional shared memory. The maximum number of pairs is half the number of volumes
shown, when primary volumes and secondary volumes are in a one-to-one relationship.
For example, if additional shared memory is not installed, since the number of volumes is 16,384,
then the number of pairs you can create is 8,192. This example assumes one secondary volume
per primary volume. If there are more secondary volumes than primary volumes, then the number
of allowed pairs decreases.
However, for Extension 1 and Extension 2, the maximum number of pairs is 16,384, regardless
of the total number of system volumes.
Table 1 Differential tables, pair tables, additional shared memory
Number of system
volumes Number of pair tables Number of diff. tables Additional shared memory
16,384 8,192 26,176 Base (No additional shared memory)
65,536 16,384 104,768 Extension 1
65,536 16,384 209,600 Extension 2
You can determine the maximum number of pairs that can be created on your system by calculating
the number of differential and pair tables your system needs to create Business Copy pairs. This
number must be equal to or less than the difference of the total number of differential and pair
tables in the storage system, minus the number of tables being used by the other products (for
example, Compatible FlashCopy).
The following software products also use differential tables:
•
Business Copy Z
•
Compatible FlashCopy
•
Compatible FlashCopy SE
•
Auto LUN
•
Snapshot
The following software products also use pair tables:
•
Business Copy Z
•
Auto LUN (using migration plans)
NOTE: You can use RAID Manager’s inqraid command to query the number of the differential
tables required when you create Business Copy pairs, though not for creating Business Copy Z
pairs. For Business Copy, you can also query the number of differential tables not used in the
storage system with this command. For details about the inqraid command, see the HP XP P9000
RAID Manager User Guide.
14 Requirements and planning