How Solaris Wait I/O is Calculated and What it Means (Doc ID 1003563.1)

Last updated on AUGUST 01, 2016

Applies to:

Solaris Operating System - Version 8.0 to 9 9/05 HW U9 [Release 8.0 to 9.0]
All Platforms

Goal

As the Wait I/O figure (iowait kstat) was deprecated in Solaris 10 onwards (defined as 0), the information in this document is only relevent to Solaris 9 and earlier.

The Wait I/O figure is one of the most misunderstood figures that we deliver in tools like mpstat and iostat.
This document addresses how the Wait I/O figure is calculated so the numbers may be used more rationally.

In general, if you are attempting to get a full idle system figure, you should add both the Wait I/O and Idle figures. While both activities are taking place, the CPU is idle.

A high Wait I/O figure does not necessarily mean a heavily overloaded system. Such simplification could misrepresent what is really going on.

Solution

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