HP XP RAID Manager Software - Manual (Page 16)

Using differential tables, use the following workflow to find the maximum number of pairs allowed
on your system:
1. The number of differential tables required for each pair.
2. The maximum number of pairs your system supports based on the number of differential tables
in the storage system. To calculate the number of differential tables that are unused and
available for SS pairs on the storage system, use the following calculation:
IMPORTANT: (The number of differential tables used by all other
software applications on the storage system) - (The total number of
differential tables that are available on the storage system)
1. Calculate the number of differential tables required for one SS pair (O) using the following
formula:
NOTE: “ceil” indicates that you must round up the result within the parenthesis () that follows.
ceil((X ч 256) ч Z)
where:
X = Capacity of the volume in kilobytes.
Z = Number of slots that a differential table can manage (639 × 32).
Round up to the nearest whole number.
Example:
(16,777,216 kB ч 256) ч (639 x 32)= 3.19523, which rounds up to four.
In this example, you must create four differential tables to create one SS pair.
2. Calculate the maximum number of SS pairs using the following formula:
T ÷ D = M
where:
T = Total number of differential tables.
D = Number of differential tables required for one SS pair.
M = Maximum number of SS pairs.
Example: This example assumes that no other software application is using differential tables, and
that the number of differential tables is 57,600.
576,00 ÷ 4 = 14,400
In this example, the maximum number of pairs allowed for SS is 14,400 pairs.
NOTE: For an SS pair, one pair consists of a P-VOL and up to 64 V-VOLs. Generations of
snapshots do not apply when you perform differential table calculations.
On the example system, you can create a maximum of 6,544 SS pairs based on differential tables.
Calculating maximum SS pairs based on shared memory workflow
Shared memory capacity for the V-VOL management area depends on additional shared memory.
You can check the pool management block and pool association shared memory capacity in the
Snapshot window.
For more information about this window, see (page 123) .
16 Business Copy/Snapshot planning and design