IBM DS8000 manual Hot spot avoidance

For example, in the zSeries environment, the RMF™ RAID rank report can be used to investigate RAID rank saturation when the DS8000 is already installed in your environment. New counters will be reported by RMF that will provide statistics on a volume level for channel and disk analysis.

In an open system environment the iostat command is useful to determine whether a system’s I/O load is balanced or whether a single volume is becoming a performance bottleneck. The tool reports I/O statistics for TTY devices, disks, and CD-ROMs. It monitors I/O device throughput and utilization by observing the time the disks are active in relation to their average transfer rates. The vmstat utility may also be used to take a quick snapshot or overview of the system performance.

9.6.8 Hot spot avoidance

Workload activity concentrated on a limited number of RAID ranks will saturate the RAID ranks. This may result in poor response times, so balancing I/O activity across any disk system is important. Spreading your I/O activity evenly across the available DS8000s will enable you to optimally exploit the DS8000 resources, thus providing better performance. I/O activity attributes to consider include spreading I/O activity across:

￿The two servers of the DS8000

￿The loops of the DS8000

￿All available RAID ranks

￿Across multiple DS8000s

188DS8000 Series: Concepts and Architecture