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 secondary volumes to a primary volume 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 during the create, split, and resync
operations.)
•
Load sharing on parity groups.
A parity group should contain an even distribution of primary volumes and secondary
volumes, rather than a concentration of one or the other. ◦
◦ When multiple pair operations are to be performed simultaneously, the pairs should be
in different parity groups.
◦ For copy pace, specify Slower when you create, split, or resynchronize.
◦ When you need 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 secondary volumes to newly installed parity groups.
•
When using multiple software products simultaneously. If you are using more than one software
product at the same time, ensure that your storage system is configured for optimal performance
(for example, sufficient cache). Contact the HP Technical Support. Concurrent use affects the
performance and the operation of the other software products.
•
When using AIX host servers. Best performance results when primary volumes are located on
one AIX host server and paired secondary volumes on another. The problem with using one
AIX host server for both primary volumes and secondary volumes is that during the paircreate
or pairresync operation, the primary and secondary volumes have the same PVID. If the host
server reboots when this is the case, it can mis-identify the volumes and identify the secondary
volume as the primary volume after rebooting.
•
Preparing for resynchronization by Quick Restore. During a quick restore operation, in which
the contents of the primary and secondary volumes 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 primary and secondary volumes
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.
Refer to the HP XP P9000 Performance for Open and Mainframe Systems User Guide for
more information on settings.
CAUTION: Do not perform the Quick Restore when the primary and secondary volumes are in
different CLPRs, otherwise the two volumes will be reversed when the operation completes.
18 Requirements and planning