Can sar be trusted?

[Martin Robinson]

I have an rp7410, 2 processor, HPUX11.11i. We run MeasureWare and Glance to collect statistics. A third party asked for the output of sar -v, specifically the %wio column, in an attempt to diagnose throughput problems. It showed about 80% for the period of measurement. However TOP showed 80% idle for the same period, and Measureware showed the GBL_DISK_SUBSYSTEM_QUEUE as about 1. sar -d shows disk queues as consistently below 0.50

So, is there a MeasureWare stat that is comparable to sar -u %wio?

Why is sar -u reporting 80% %wio when TOP shows it as 80% idle?

Puzzled.

[Steven E. Protter]

sar is the reliable, old horse that runs across various unix platforms.

It is as far as I know extremely reliable. Check for patches, install them and try again.

Every time, my sar data collection script indicated bottlenecks, they were real, recurring and had to be dealt with.

Attaching the script as a reference point.

SEP

[Dietmar Konermann]

Some short notice on 'Why is sar -u reporting 80% %wio when TOP shows it as 80% idle? '

Why not? :)

%wio
idle with some process waiting for I/O (only block I/O, raw I/O, or VM pageins/swapins indicated);

Essentially sar distinguishes between idle and idle while waiting for IO. From a CPU perspective (which is reported by top) both states are idle.

Best regards...
Dietmar.

[Paula J Frazer-Campbell]

Hi

Top output is based on an average whereas sar is a moment by moment base.

Paula

[Wodisch]

Hi,

*all* the performance measurement tools have blind spots, that's just one reason why you usually consult multiple of those...

FWIW,
Wodisch

[Decio Miname]

Dietmar is right, let's separate things.

There are perftuning-usable commands that consider WIO separately (like some flags of sar, like the summarized -u), and other don't (like top).

For the tools that don't report WIO explicitly, IDLE must be considered as a sum of "really IDLE" (really nothing to do) and WIO (nothing to do because I/O have not responded yet).

D.

[Sunil Sharma_1]

Hi,
sar is the best and only reliable utility to find out server resources utilization infact some thired paty tools are using the same sar o/p to generat reports and all.

The difference between top and sar is becoz when sar show %wio means it's waiting for data from disk (generally) but in this case CPU is Idle which reports by top. so top and sar use different way to show the things.
You can run sar -q and check for the runq-sz value it says about Average length of the run queue(s) of processes this will show exactely how many processes are in the queue.

Sunil

[Khalid A. Al-Tayaran]

Hi,

sar is very fine. Also add to that iostat nad vmstat.