Date: Wed, 29 May 2013 09:16:17 -0600 From: Ian Lepore <ian@FreeBSD.org> To: Oliver Fromme <olli@lurza.secnetix.de> Cc: killing@multiplay.co.uk, freebsd-stable@FreeBSD.org Subject: Re: 9.1-stable: ATI IXP600 AHCI: CAM timeout Message-ID: <1369840577.1258.45.camel@revolution.hippie.lan> In-Reply-To: <201305291421.r4TELY8p042536@grabthar.secnetix.de> References: <201305291421.r4TELY8p042536@grabthar.secnetix.de>
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On Wed, 2013-05-29 at 16:21 +0200, Oliver Fromme wrote: > Steven Hartland wrote: > > Have you checked your sata cables and psu outputs? > > > > Both of these could be the underlying cause of poor signalling. > > I can't easily check that because it is a cheap rented > server in a remote location. > > But I don't believe it is bad cabling or PSU anyway, or > otherwise the problem would occur intermittently all the > time if the load on the disks is sufficiently high. > But it only occurs at tags=3 and above. At tags=2 it does > not occur at all, no matter how hard I hammer on the disks. > > At the moment I'm inclined to believe that it is either > a bug in the HDD firmware or in the controller. The disks > aren't exactly new, they're 400 GB Samsung ones that are > several years old. I think it's not uncommon to have bugs > in the NCQ implementation in such disks. > > The only thing that puzzles me is the fact that the problem > also disappears completely when I reduce the SATA rev from > II to I, even at tags=32. > It seems to me that you dismiss signaling problems too quickly. Consider the possibilities... A bad cable leads to intermittant errors at higher speeds. When NCQ is disabled or limited the software handles these errors pretty much transparently. When NCQ is not limitted and there are many outstanding requests, suddenly the error handling in the software breaks down somehow and a minor recoverable problem becomes an in-your-face error. I'm not saying any of the foregoing is true, just that you should consider the possibility that you're dealing with multiple problems which are only loosely coupled, but together can seem like a single more serious problem. You don't know enough yet to casually dismiss anything. -- Ian
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