problems with AHCI on FreeBSD 8.2

[Victor Balada Diaz]

On Tue, Feb 14, 2012 at 06:17:19PM +0100, Harald Schmalzbauer wrote:
>  schrieb Jeremy Chadwick am 14.02.2012 17:50 (localtime):
> > On Tue, Feb 14, 2012 at 04:55:10PM +0100, Claudius Herder wrote:
> >> Hello,
> >>
> >> I have got a quite similar problem with AHCI on FreeBSD 8.2 and it still
> >> persists on FreeBSD 9.0 release.
> >>
> >> Switching from ahci to ataahci resolved the problem for me too.
> >>
> >> I'm using gmirror for swap, system is on a zpool and the problem first
> >> occurred during a zpool scrub, but it is easily reproducible with dd.
> >>
> >> The timeouts only occur when writing to disks, dd if=/dev/ada{0|1}
> >> of=/dev/null is not an issue.
> >> Sometimes I need to power off the server because after a reboot one disk
> >> is still missing.
> >>
> >> I really would like to help in this issue, so let me know if you need
> >> any more information.
> > I find it interesting that, at least so far, the only people reporting
> > problems of this type with the ahci.ko driver are people using Samsung
> > disks.  The only difference is that your models are F1s while the OPs
> > are F2s.
> 
> I saw such timeouts long ago and mav@ had a look at my postings and he
> mentioned it could be a NCQ problem.
> I suspected the disks firmware.
> I never tracked it down further, because after replacing the Samsung (F3
> in that case) disks with hitachi ones solved all my problems and gave a
> big performance kick as well (with zfs).
> You can find the discussion here:
> http://lists.freebsd.org/pipermail/freebsd-stable/2010-February/055374.html
> 

You gave me a good idea: try to disable NCQ and see if that's the fault. So
i went and applied the attached patch. After it, i can no longer reproduce
the issue with ahci driver.

I know this is not a solution because it disables NCQ at controller level
instead of disk level, but at least we know for sure where the problem is.

I think the solution would be to add a new quirk ADA_Q_NONCQ in sys/cam/ata/ata_da.c.
Quirks infraestructure is already built, so adding a new quirk for this seems
easy.

Is someone interested? Do you think there is a better solution?

If someone is interested i can build a patch to add ADA_Q_NONCQ quirk and add my drives
to it.

Regards.
-- 
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