HP XP RAID Manager Software - Manual (Page 19)

Use the following formula to calculate the capacity:
Capacity (bytes) of shared memory used by the P-VOL = ceil (ceil (P-VOL capacity (KB)/256 (KB))/2,048) X 8,736
+ ceil (ceil (ceil (P-VOL capacity (KB)/256 (KB))/2,048)/1,024) X 8,736
Calculating maximum pairs based on pair tables
SS and Compatible FlashCopy (FC Z) pairs use pair tables. A pair table keeps track of the status
for a pair. You use one pair table for each pair.
To calculate the maximum number of SS pairs you can create, use the following formula:
Max. num. SS pairs = The number of pair tables - The number of FC Z
pairs on the storage system
A storage system contains 1,048,575 pair tables. On the example system, you can create a
maximum of 1,048,575 SS pairs based on pair tables.
Determining maximum pairs allowed on your system
To determine the maximum number of SS pairs your system supports, use the example calculations
described in the following sections:
•
“Calculating maximum SS pairs based on differential tables workflow” (page 15) .
•
“Calculating maximum SS pairs based on shared memory workflow” (page 16) .
•
“Calculating maximum pairs based on pair tables” (page 19) .
Planning for splitting pairs in consistency groups
Use the At-Time Split operation to split pairs in a consistency group at a pre-determined time. Use
this operation for multiple pairs and for multiple pairs whose P-VOLs are shared with Continuous
Access Synchronous (Cnt Ac-S) or Continuous Access Journal (Cnt Ac-J) S-VOLs.
Use the following list to plan for splitting pairs in consistency groups:
1. Note the requirements in “Requirements and restrictions for the At-Time Split operation”
(page 19) .
2. Before defining consistency groups for the pairsplit operation, read the information in “Pair
inclusion in At-Time Split operations workflow” (page 20) .
3. To share SS P-VOLs with Cnt Ac-J or Cnt Ac-S S-VOLs within a storage system, read the
information in
“Consistency maintenance workflow when sharing SS P-VOLs with Cnt Ac-J or
Cnt Ac-S volumes” (page 20) .
Requirements and restrictions for the At-Time Split operation
Note the following requirements and restrictions when setting up to perform an At-Time Split
operation:
•
You must include the pairs in the same consistency group.
•
The pairs must have a status of “PAIR”. For more information about pair status, see “Pair status
definitions” (page 44) .
•
If you want to make changes to the pair, make the change in the same consistency group
according to the copy group.
•
Registering the At-Time Split operation:
You can split or delete pairs while registering the At-Time Split. If you create a pair, split
a pair, or resynchronize a pair, the split time is rejected. To perform one of these
operations, reset the registration of the At-Time Split. ◦
◦ Switching off the power resets the pre-determined split time.
◦ Performs the At-Time Split operation when a read/write request—with a time stamp past
the specified Split time—is received. Run a read/write request to prevent delays in the
Planning for splitting pairs in consistency groups 19