You can generally maximize the performance of an application by
spreading the I/O load across clusters, arrays, and device adapters in the
storage unit.
During an attempt to balance the load within the storage unit, placement
of application data is the determining factor. The following resources are
the most important to balance, roughly in order of importance:
- Activity to the RAID disk groups. Use as many RAID disk groups as possible
for the critical applications. Most performance bottlenecks occur because
a few disks are overloaded. Spreading an application across multiple RAID
disk groups ensures that as many disk drives as possible are available. This
is extremely important for open-system environments where cache-hit ratios
are usually low.
- Activity to the clusters. When selecting RAID disk groups for a critical
application, spread them across separate clusters. Because each cluster has
separate memory buses and cache memory, this maximizes the use of those resources.
- Activity to the device adapters. When selecting RAID disk groups within
a cluster for a critical application, spread them across separate device adapters.
- Activity to fibre-channel or FICON ports. Use the IBM System Storage™ Multipath
Subsystem Device Driver (SDD) or similar software for other platforms to balance
I/O activity across fibre-channel ports.
Note: For information about SDD, see IBM System Storage Multipath
Subsystem Device Driver User's Guide. This document also describes the
product engineering tool, the ESSUTIL tool, which is supported in the pcmpath
commands and the datapath commands.