Strange disk problem
attilio at freebsd.org
Tue Apr 20 12:29:15 UTC 2010
2010/4/20 David Ehrmann <ehrmann at gmail.com>:
> Initially, I noticed a problem where reading a file on this machine seemed
> to stop--something like a video would just stop playing. At first, I
> thought it was the machine, but a new motherboard, CPU, and RAM later, the
> problem persists. The network card uses a different chipset, too.
> The files are on zfs, but scrubs are fine, and zpool status lists no errors
> of any kind. Trying to reproduce the problem, I set up a script that
> reading a random 1M block every 60 seconds off the drive backing zfs.
> That's when I noticed something: one disk seems to be causing the problems.
> I logged the dd times, and some of them were huge--more than a minute. The
> times on the other disk in the mirrored vdev were low.
> I've only seen the problem when I have a vm's disk image hosted on the
> machine. That said, the network interface is configured at 100mbps, so
> there's no reason for that to saturate the disk's throughput. Top reports
> that almost 20% of the CPU is going towards interrupts. I can read a file
> off the zfs pool at over 50MB/s, so that shouldn't be a problem. One thing
> I'm wondering is why the disk read doesn't timeout quickly? At least that
> way zfs could try to use the other drive in the mirrored vdev.
> Any ideas? One thing I should try is switching the drive, see if the
> problem follows the disk or stays with the lowest /dev/adX device. I'm
> using geli, but the read problems happen with both /dev/adX AND
> /dev/adX.eli., so I don't think that's it. I've seen the problem with
> Samba, NFS, and dd.
do you think you are willing to re-create the problem and do a PMC
analysis on it?
(If you need any guidance let me know, I will be happy to give it).
Peace can only be achieved by understanding - A. Einstein
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