[mythtv-users] Odd i/o issues

Yeechang Lee ylee at pobox.com
Wed Jan 14 08:14:43 UTC 2009


Michael D. O'Brien <obrienmd at gmail.com> says:
> -on the backend, iostat -xk 1 shows something interesting: my raid5
> array participants are all being used, but it seems that two of the
> drives hover around 10% usage, while one is constantly pegged at
> 100% usage.  Is this normal behavior in iostat -xk for a raid5
> array?  it seems odd to me.

It is normal if the drive with 100% usage rotates every few
seconds. If it's always the same drive, you see unusual I/O issues,
and you use smartd, check the drive with smartctl -a /dev/sdx and see
if a self-test is going on. If there is one, cancel it with smartctl
-X /dev/sdx.

smartd can be configured to schedule long or short self-tests using
drives' built-in functionality. On my RAID 6 array I've noticed an
issue in which sometimes one of the drives will get "stuck" in a long
self-test at 10% remaining, taking utilization as viewed in iostat to
100% and causing recording and writing I/O issues of the kind you
describe. I don't know if it's an issue with smartd or the (Western
Digital RE2) firmware; meanwhile I only schedule daily short
self-tests on the array.

-- 
Frontend:		P4 3.0GHz, 1.5TB software RAID 5 array
Backend:		Quad-core Xeon 1.6GHz, 6.6TB sw RAID 6
Video inputs:		Four high-definition over FireWire/OTA
Accessories:		47" 1080p LCD, 5.1 digital, and MX-600


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