HP XP P9500 Storage - Manual (Page 15)

Calculating the number of differential tables and pair tables
Calculations in the following sections assume only Business Copy is used in the system.
The emulation type of your volumes affects the number of differential and pair tables.
To calculate the number of differential and pair tables for OPEN-V
Total number of differential tables per pair = (volume capacity KB ÷ 48) + (number of the control
cylinders* Ч 15) ч (20,448**)
* See the following table.
** Number of slots that can be managed by a differential table
Round up the total number to the nearest whole number. For example, if the number of the cylinders
of the divided volume is 2,403,360 KB, the calculation of the total number of the differential tables
is as follows.
(2,403,360 ч 48 + 8 Ч 15) ч 20,448 = 2.4545...
When you round up 2.4545 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.
To calculate the number differential and pair tables for OPEN-V
Total number of the differential tables per pair = (volume capacity KB ч 256) ч 20,448*
* 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 number of the cylinders
of the divided volume is 3,019,898,880 KB, the calculation of the total number of the differential
tables is as follows.
(3,019,898,880 ч 256) ч 20,448 = 576.9014...
When you round up 576.9014 to the nearest whole number, it becomes 577. In this example,
the total number of the differential tables for one pair is 577. Because one pair table is used for
up to 36 differential tables, the total number of the pair tables for a pair is 17. (Only OPEN-V can
use more than one pair table per pair.)
Table 2 Control cylinders per emulation type
Number of control cylinders Emulation type
8 (5,760KB) OPEN-3
27 (19,440KB) OPEN-8, OPEN-9
19 (13,680KB) OPEN-E
9 (6,480KB) OPEN-K
7 (5,040KB) OPEN-L
0 (0KB) OPEN-V
If the volume is divided by VLL, use the volume capacity after the division. Note that VLL operations
cannot be performed on OPEN-L volumes.
Having determined the number of differential and pair tables required per pair on your storage
system, you can now calculate the maximum number of pairs.
Calculating maximum number of pairs
Finding the number of pairs that can be created on your system depends on whether you use LUSE
volumes or not. Two calculations are provided below, one without LUSE, and one with LUSE.
Planning pair volumes 15