HP XP P9500 Storage - Manual (Page 18)

Planning for performance
Pair operations affect I/O performance on the storage system. The following information is provided
to help calibrate your system:
•
Performance versus number of pairs. Compare the importance of performance with the number
of pairs and copy pace (rate at which data is copied).
◦ Assigning multiple S-VOLs to a P-VOL uses more system resources and lowers performance.
◦ The slower the copy pace, the less impact on I/O performance; a fast pace has a greater
impact on performance. (You assign copy pace while creating, splitting, and
resynchronizing pairs.)
•
Load sharing on parity groups.
A parity group should contain an even distribution of P-VOLs and S-VOLs, rather than a
concentration of one or the other. ◦
◦ If you plan to perform multiple pair operations simultaneously, place the pairs in different
parity groups.
◦ For copy pace, specify Slower when you create, split, or resynchronize.
◦ If you plan to perform a copy operation on multiple pairs on the same parity group,
perform the operation on one pair at a time.
◦ If the system is overloaded, increase parity groups, cache, channel adapters (CHAs),
and/or disk adapters (DKAs). Assign S-VOLs to newly installed parity groups.
•
Preparing for resynchronization by Quick Restore. During a Quick Restore operation, in which
the contents of the P-VOL and S-VOLs are swapped, the RAID levels, HDD types, and Cache
Residency settings of the two volumes are also exchanged. To avoid performance impact,
consider the following:
◦ Both pair volumes should have the same RAID level and HDD type before performing the
Quick Restore operation. You can resume the original RAID levels after the Quick Restore
by again splitting the pair and performing the Quick Restore.
◦ Set the same Cache Residency settings (locations) for the P-VOL and S-VOLs before the
Quick Restore operation.
Alternatively, you can release Cache Residency settings before the Quick Restore
operation, then reset them when the operation is completed.
For more information about settings, see the HP XP P9000 Performance for Open and
Mainframe Systems User Guide.
CAUTION: Do not perform the Quick Restore when the P-VOL and S-VOLs are in different CLPRs,
otherwise the two volumes will be reversed when the operation completes.
At-Time Split at a specific time
With a consistency group, you perform tasks and change the pair status on a group of pairs.
With the At-Time Split feature, you define a specific time to split pairs in a consistency group. This
allows you to copy data from the S-VOLs in the consistency group to the T-VOLs simultaneously.
The T-VOLs will contain the same data as the S-VOLs when the operation is performed.
18 Requirements and planning