topic Re: sar -d data in Operating System - HP-UX

sar -d data

Dean Irving — Fri, 01 Mar 2002 12:04:51 GMT

Don't understand how the 'avwait' time came be higher than the 'avserv' time? What's the better indicator of 'busy-ness' of a disk? Why?

Re: sar -d data

Thierry Poels_1 — Fri, 01 Mar 2002 12:14:26 GMT

Hi,

avwait
indicates the average time in ms that a disk job waited in queue (before really starting disk I/O) ... as work starts stacking up the avwait increases indicating processes are waiting for work on that drive.

avserv
indicates the average time in ms that a disk job took to complete.... (=effective disk I/O)

regards,
Thierry.

Re: sar -d data

Steven Sim Kok Leong — Fri, 01 Mar 2002 12:26:41 GMT

Hi,

If the jobs are processed on average (avserv) very slowly and that a job waits very long for its turn to be served in the queue on average (avwait), it is indicative that the queue of jobs is clearing too slowly, like the queue of people in front of a foodstall - very busy.

Hope this helps. Regards.

Steven Sim Kok Leong

Re: sar -d data

Dean Irving — Fri, 01 Mar 2002 12:52:39 GMT

So, if 'avwait' spikes occassionally to 120-180ms, but 'mean' of the 'avwait' values hoovers around 70-80ms and 'avserv' time is farily constant at 20-30ms, does this indicate a problem? Drives in question are the mirrored vg00 (i.e., the 'root' drives). System is SuperDome running 11.11/64

Re: sar -d data

Thierry Poels_1 — Fri, 01 Mar 2002 13:01:33 GMT

hmmmz,
Superdome, as in recent fast hi-tec hardware?!?! Yep, I would say you have a problem. Your figures are way to high. Try to find the cause of the problem: runaway process, patch required, swapping, .... Use glance to trace the heaviest I/O process. VG00 normally does not contain application data, so shouldn't be overloaded at all.

good luck,
Thierry.