
The output reports the following:
The %tm_act column indicates the percentage of the measured interval time that the device was busy.
The Kbps column shows the average data rate, read and write data combined, of this device.
The tps column shows the transactions per second. Note that an I/O transaction can have a variable transfer size. This field may also appear higher than would normally be expected for a single physical disk device.
The Kb_read and Kb_wrtn columns show the total amount of data read and written.
iostat can also be issued for continuous monitoring with a given number of iterations and a monitoring period. It will then print a report like that in Example
Example
Example: A-2 SUN Solaris iostat output
#iostat |
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extended disk statistics |
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disk | r/s | w/s | Kr/s | Kw/s wait actv svc_t %w %b | |||||
fd0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0 | 0 |
sd1 124.3 | 14.5 | 3390.9 | 399.7 | 0.0 | 2.0 | 15.7 | 0 | 90 | |
sd2 | 0.7 | 0.4 | 13.9 | 4.0 | 0.0 | 0.0 | 7.8 | 0 | 1 |
sd3 | 0.4 | 0.5 | 2.5 | 3.8 | 0.0 | 0.1 | 8.1 | 0 | 1 |
sd6 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 5.8 | 0 | 0 |
sd8 | 0.3 | 0.2 | 9.4 | 9.6 | 0.0 | 0.0 | 8.6 | 0 | 1 |
sd9 | 0.7 | 1.3 | 12.4 | 21.3 | 0.0 | 0.0 | 5.2 | 0 | 3 |
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The implementation of the iostat command is different for every UNIX variant. It also offers many different options and parameters. Refer to your system documentation and the iostat man page for more information.
System Activity Report (SAR)
The System Activity Report (SAR) provides a quick way to tell if a system is I/O bound. SAR has numerous options, providing paging, TTY, CPU busy, and many other statistics.
One way you can run sar is by specifying a sampling interval and the number of times you want it to run.
This is shown in Example
times with a two second interval. To check whether a system is I/O bound, the important column to look at is %wio. The %wio indicates the time spent waiting on I/O from all disks,
both internal and external. Here, too, the first line represents the average since boot time and should be discarded.
302DS6000 Series: Concepts and Architecture