Solaris

Execute the following UNIX command to report on I/O Statistics:

The meaning of the options used here are:

• x: Reports on extended disk statistics. By default, disks are identified by instance names such as ssd23 or md301. Combining the x option with the -n option causes disk names to display in the cXtYdZsN format, more easily associated with physical hardware characteristics. If no output display is requested (no -x, -e,-E), -x is implied.


• t: Report the number of characters read and written to terminals per second.


• n: Display names in descriptive format. For example, cXtYdZ, rmt/N, server:/export/path.

Performance Goals

Signficant bottleneck threshold is: %b > 20% and asvc_t in (20ms, 30ms)

Critical bottleneck threshold is: %b > 20% and asvc_t > 30ms

where

• svc_t is the average service time in ms of the disk


• %b is the percentage of tike the disk is busy, that is, transaction in progress.

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AIX

%tm_act - percentage of time disk is busy

Note: High tm_act percentage can indicate a disk bottleneck.

%iowait: % of time the CPU is idle while waiting on local I/O.

The time is attributed to iowait when no processes are ready for the CPU but at least one process is waiting on I/O. The high% of iowait time indicates that disk I/O is a major contributor to the delay in execution of processes. In general, if system slowness occurs and %iowait in (20,25)% or higher, investigate disk bottleneck.

When %tm_act or time active for a disk is high, noticeable performance degradation can occur.

On some systems, a %tm_act > 35% for one disk can noticeably slow performance.

• Look for busy vs idel drives, moving data from more busy to less busy drives may alleviate a disk bottleneck.
• Check for page because paging to and disk will contribute to the I/O load.