HP XP RAID Manager Software - Manual (Page 15)

The maximum number of SS pairs supported on a system is the lowest value based on the following
calculations:
•
The number of differential tables.
For more information about calculating based on differential tables, see “Calculating maximum
SS pairs based on differential tables workflow” (page 15) .
•
The shared memory capacity for the V-VOL management area.
For more information about calculating based on shared memory, see “Calculating maximum
SS pairs based on shared memory workflow” (page 16) .
•
Number of pair tables.
For more information about calculating based on pair tables, see “Calculating maximum pairs
based on pair tables” (page 19) .
If you are creating external volumes or Fast Snap (FS), THP, or Smart V-VOLs in the storage system,
see
“Calculating SS pairs when creating external volumes or V-VOLs” (page 15) .
Calculating SS pairs when creating external volumes or V-VOLs
If you are creating external volumes or FS, THP, or Smart V-VOLs in the storage system, the maximum
number of SS pairs you can create is the lowest value based on the following calculations and no
more than 63,232 pairs:
•
The value of the calculations for calculating the number of SS pairs.
For more information about calculating the number of SS pairs, see “Calculating the number
of Snapshot pairs” (page 14) .
•
Max. num. SS pairs = Num. of external volumes + Num. of FS, THP,
Smart, and SS V-VOLs
Calculating maximum SS pairs based on differential tables workflow
Differential tables keep track of the updates that take place in pairs. The number of these tables a
pair requires depends on the size of the volumes.
A base that does not have shared memory has 26,176 differential tables. The remaining number
of differential tables on a system is determined by the amount of shared memory that is installed
on your system. For more information about determining this amount, see
“Determining maximum
pairs allowed on your system” (page 19) .
When you use SS, the shared memory level is COW 1 with Extension 1 and Extension 2. The
following table shows the shared memory level combinations and the number of differential tables
that are associated with them.
Differential tables required Combination
26,176 tables Base with no shared memory
104,768 tables Extension 1
209,600 tables Extension 2
The following software applications also use differential tables:
•
BC/SS
•
BC Z
•
Compatible FlashCopy
•
Auto LUN V2
Calculating the number of Snapshot pairs 15