HP XP P9500 Storage - Manual (Page 17)

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. Rounding up
2.4537 to the nearest whole number changes it to 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.
Table 2 Control Cylinders per Emulation Type
Number of Control Cylinders Emulation Type
7 3380-3, 3380-3A, 3380-3B, 3380-3C
6 3390-3, 3390-3A, 3390-3B, 3390-3C
25 3390-9, 3390-9A, 3390-9B, 3390-9C
23 3390-L, 3390-LA, 3390-LB, 3390-LC
53 3390-A, 3390-M, 3390-MA, 3390-MB, 3390-MC
NOTE: You cannot perform VLL operations 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
With the calculation for the number of differential and pair tables done in the previous section,
you can determine the maximum number of pairs your storage system can support.
To calculate the maximum number of pairs allowed on your system
Use the following formula:
Σ(α) ≤ (β)and Σ(γ) ≤ (δ)
where:
•
Σ(α) is the total number of differential tables per pair (per previous calculation).
•
(β) is the number of differential tables available in the system (see Table 1 (page 16) ).
•
Σ(γ) is the total number of pair tables per pair (per previous calculation).
•
δ is the number of pair tables available in the system ( Table 1 (page 16) ).
(β) and (δ) will differ according to the installed additional shared memory for differential
tables.
For example, if you are to create 10 pairs of 3390-3 volumes and 20 pairs of 3390-L volumes in
a storage system that has 26,176 differential tables, the following equation would be used to
calculate Σ(α) and Σ(γ):
Σ(α): (3 x 10) + (24 x 20) = 510
Σ(γ): (1 x 10) + (1 x 20) = 30
Since 510 is smaller than 26,176, and 30 is smaller than 8,192, it meets the equation, Σ(α) ≤
(β) and Σ(γ) ≤ (δ), thus insuring that 10 pairs of 3390-3 volumes and 20 pairs of 3390-L volumes
can be created.
Planning pair volumes 17