More IO identification problems

[Andriy Gapon]

on 26/11/2010 08:05 Adam Vande More said the following:
> As a follow-up, after applying both patches presented in this thread(FreeBSD
> 8.2-PRERELEASE #5: Thu Nov 25 19:14:00 CST 2010),
> 
> http://lists.freebsd.org/pipermail/freebsd-stable/2010-November/060298.html
> 
> "top -m io" now displays much more info and is generally consistent with
> gstat in that IO spikes occer around the same time.  However, gstat and "top
> -m io" are still not displaying any stats for 90%+ of my hard drive
> indicator light blinks.  Since the issue effects gstat as well, it doesn't
> seem like it could be related to ZFS.  When the system is basically idling,
> the only consistent IO related entries are these;
> 
>     6 root           15      0      1     12      0     13  20.00%
> {l2arc_feed_threa}
>     6 root           15      0      1     12      0     13  20.00%
> {arc_reclaim_thre}
>     6 root           15      0      1     12      0     13  20.00% {zvol
> zoot/usr/ho}
>     6 root           15      0      1     12      0     13  20.00%
> {txg_thread_enter}
>     6 root           15      0      1     12      0     13  20.00%
> {txg_thread_enter}
> 
> Entries like these occur like clockwork on 30 sec intervals.  My theory here
> is that since the ZVOL has UFS + SU, this is causing a sync?
> 
> What I'm trying to diagnose is a much more frequent hard drive access which
> occurs on approximately 2 sec intervals.  I timed this by pinging localhost
> and comparing the response to the blinks.  It's very consistent although not
> completely so as once in awhile the blink occurs every second.  If I listen
> carefully I can hear increased drive activity during many of these intervals
> so the indicator light seems to be working correctly.
> 
> If anyone has ideas or tests they'd like me to run, it would be appreciated.
> 

Perhaps it's some external component?
E.g. hald is known to perform some disk/media checks every two seconds.

-- 
Andriy Gapon