Planning Number Of Pairs; Calculating Number Of Differential, Pair Tables - HP StorageWorks P9000 User Manual

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.
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 P-VOLs and S-VOLs 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 S-VOL per P-VOL. If
there are more S-VOLs than P-VOLs, 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 2 Differential tables, pair tables and additional shared memory
Additional Shared Memory for Business
Copy
Base (No additional shared memory)
Extension 1
Extension 2
You can determine the maximum number of pairs which 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
such as Compatible FlashCopy.
The following program products also use differential tables:
Compatible FlashCopy
Auto LUN
Snapshot
The following program products also use pair tables:
Compatible FlashCopy
Auto LUN (using migration plans)
Calculations in the following sections assume only Business Copy is used in the system.
NOTE: You can use the 's inqraid command to query the number of differential tables required
when you create Business Copy pairs. You can also query the number of the differential tables not
used in the storage system by using this command. For details about the inqraid command, see
the HP StorageWorks P9000 RAID Manager User Guide.

Calculating number of differential, pair tables

The emulation type of your volumes affects the number of differential and pair tables.
12 Requirements and planning
Number of Diff. Tables Number of Pair Tables
26,176 8,192
104,768 16,384
209,600 16,384
Number of System
Volumes
16,384
65,536
65,536