Any objections/comments on axing out old ATA stack?

[Victor Balada Diaz]

On Sun, Mar 31, 2013 at 03:02:09PM -0600, Scott Long wrote:
> 
> On Mar 31, 2013, at 7:04 AM, Victor Balada Diaz <victor at bsdes.net> wrote:
> 
> > On Wed, Mar 27, 2013 at 11:22:14PM +0200, Alexander Motin wrote:
> >> Hi.
> >> 
> >> Since FreeBSD 9.0 we are successfully running on the new CAM-based ATA 
> >> stack, using only some controller drivers of old ata(4) by having 
> >> `options ATA_CAM` enabled in all kernels by default. I have a wish to 
> >> drop non-ATA_CAM ata(4) code, unused since that time from the head 
> >> branch to allow further ATA code cleanup.
> >> 
> >> Does any one here still uses legacy ATA stack (kernel explicitly built 
> >> without `options ATA_CAM`) for some reason, for example as workaround 
> >> for some regression? Does anybody have good ideas why we should not drop 
> >> it now?
> > 
> > Hello,
> > 
> > At my previous job we had troubles with NCQ on some controllers. It caused
> > failures and silent data corruption. As old ata code didn't use NCQ we just used
> > it.
> > 
> > I reported some of the problems on 8.2[1] but the problem existed with 8.3.
> > 
> > I no longer have access to those systems, so i don't know if the problem
> > still exists or have been fixed on newer versions.
> > 
> > Regards.
> > Victor.
> 
> 
> So what I hear you and Matthias saying, I believe, is that it should be easier to
> force disks to fall back to non-NCQ mode, and/or have a more responsive
> black-list for problematic controllers.  Would this help the situation?  It's hard to
> justify holding back overall forward progress because of some bad controllers;
> we do several Tbps off of AHCI controllers with NCQ enabled on FreeBSD 9.x,
> enough to make up a sizable percentage of the internet's traffic, and we see no
> problems.  How can we move forward but also take care of you guys with
> problematic hardware?
> 
> Scott

Being able to configure quirks from loader.conf for disks AND controllers would be great
and is not hard to do. If you want i can do a patch in two weeks and send it to you. That
way it's easy to test disabling NCQ and/or other things in case of hitting a bug. Also
being able to modify the configuration without a kernel recompile would be a big
improvement because we could still use freebsd-update to keep systems updated.

Anyway, my comment was not against dropping old ata code, but more on the "comments on
regresssions on the new one".

Regards.
Victor.
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