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

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 S-VOLs and T-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 T-VOL per S-VOL. If
there are more T-VOLs than S-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 Z
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
Z 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 Version 2.
The following program products also use differential tables:
Compatible FlashCopy Version 2
Auto LUN
Snapshot
The following program products also use pair tables:
Compatible FlashCopy Version 2
Auto LUN (using migration plans)
Calculations in the following sections assume only Business Copy Z is used in the system.

Calculating number of differential tables, pair tables

The emulation type of your volumes affects the number of differential and pair tables.
To calculate the number differential and pair tables for z/OS
Total number of the differential tables per pair = (the number of cylinders in a volume) + (number
of the control cylinders*) × 15 ÷ (20,448**)
* See the following table.
** Number of the slots that can be managed by a differential table
Round up the total number to the nearest whole number. For example, if the emulation type is
3390-3 and if the number of the cylinders of the volume is 3390, then the total number of the
differential tables is calculated as follows: ((3,339 + 6) x 15) ÷ 20,448 = 2.4537. When you
round up 2.4537 to the nearest whole number, it becomes 3. In this example, the total number of
the differential tables for one pair is 3. Because one pair table is used for up to 36 differential
tables, the total number of the pair tables for a pair in this example is 1.
12 Requirements and planning
Number of differential Number of pair tables
tables
26,176 8,192
104,768 16,384
209,600 16,384
Number of system
volumes
16,384
65,536
65,536