IBM DS8000 manual Vmstat, Example A-3 SAR Sample Output

Example: A-3 SAR Sample Output

# sar -u 2 5
AIX aixtest	3 4	001750154C00 2/5/03
17:58:15 %usr		%sys	%wio %idle
17:58:17	43	9	1	46
17:58:19	35	17	3	45
17:58:21	36	22	20	23
17:58:23	21	17	0	63
17:58:25	85	12	3	0
Average	44	15	5	35

As a general rule of thumb, a server with over 40 percent waiting on I/O is spending too much time waiting for I/O. However, you also have to take the type of workload into account. If you are running a video file server, serving I/O will be the primary activity of the machine and you will expect high %wio values.

A system with very busy CPUs can mask I/O wait. The definition of %wio is: Idle with some processes waiting for I/O (only block I/O, raw I/O, or VM pageins/swapins indicated). If the system is CPU busy and also is waiting for I/O, the accounting will increment the CPU busy values, but not the %wio column.

The other column headings in the example indicate:

￿%usr: Time system spent executing application code

￿%sys: Time system spent executing operating system calls

￿%idle: Time the system was idle with no outstanding I/O requests

The implementation of the sar command is different for the various UNIX variants. However, the output of sar -uis the same for all.

There are other modes to use sar, which we will not discuss further:

￿Ongoing system activity accounting via cron

￿Display previously captured data

sar offers many different options and parameters. Refer to your system documentation and the sar manpage for more information.

VMSTAT

The vmstat utility is a useful tool for taking a quick snapshot or overview of the system performance. It is easy to see what is happening with regard to the CPUs, paging, swapping, interrupts, I/O wait, and much more. There are several reports that vmstat can provide. They vary slightly between the different versions of UNIX. Refer to your system documentation and the vmstat manpage for more information.

IBM AIX

This section covers items specific to the IBM AIX operating system. It is not intended to repeat the information that is contained in other publications. We focus on topics that are not covered in the well known literature or are important enough to be repeated here.

Appendix A. Open systems operating systems specifics 347