Date: Fri, 9 Jun 2006 20:33:07 +0100 (BST) From: Chris Hedley <cbh-freebsd-current@groups.chrishedley.com> To: Doug White <dwhite@gumbysoft.com> Cc: current@freebsd.org Subject: Re: aac0: COMMAND 0xffffffffxxxxxxxx TIMEOUT AFTER xx SECONDS Message-ID: <20060609202536.Y829@aga.cbhnet> In-Reply-To: <20060609120159.I60598@carver.gumbysoft.com> References: <20060609163735.D829@aga.cbhnet> <20060609120159.I60598@carver.gumbysoft.com>
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On Fri, 9 Jun 2006, Doug White wrote: > On Fri, 9 Jun 2006, Chris Hedley wrote: >> I've been receiving this message quite a lot lately if I put my Adaptec >> 2410SA aac controller under really heavy load. A quick look at the >> archives suggests that it used to be a problem a couple of years ago, but >> was apparently fixed. Personally I've had no bother with it until a few >> months ago when I upgraded my version of -CURRENT, at which point it >> started misbehaving. > > I assume you've checked cabling and termination? Frequently, driver updates > can improve performance which means less tolerance for marginal > configurations. The 2410SA uses SATA discs (I was trying to get SCSI performance on the cheap, ever the optimist!) so I'm assuming that the cables are okay. At least there's no user-breakable termination settings for me to worry about... >> I'm also wondering if I might not be better off actually replacing the card >> with something better, or at least something better suited to FreeBSD: with >> the discs' and controller's write-caching turned off, the 2410SA is >> s-l-o-w, about 6MB/s for contiguous writes to an array (either RAID-5 or >> RAID-10) (benchmarked using the admittedly somewhat crude "dd various block >> sizes to/from a /dev entry" technique), although reads are acceptable at >> ~50-60MB/s, if not especially earth-shattering. Any suggestions (for >> something inexpensive! If money were no object I'd've gone for a SCSI-only >> system), or might I just as well stick with the 2410SA? > > 6MB/s sounds like you aren't getting any help from the card's write cache; > its having to do stripe reads to recalculate parity instead of doing full > stripe writes. Many cards disable write-back cache if the battery module > isn't present -- make sure you have one and its working. /dev accesses also > use physio so you don't get any benefit from write combining in the > filesystem layer. I've deliberately turned off write-caching because the 2410SA doesn't support battery-backed memory. I'm not sure if it's really necessary to disable it, but having experienced the odd disc crash in the past I've become a little paranoid about my data... > Also, in general, hardware RAID beats PCI RAID, hands down. In my case, software raid beats it too! I have my "fast discs" attached to an old 3960 controller and mirror them with gmirror, and the write performance is an order of magnitude better than the 2410SA, which tells me that something somewhere must be wrong. I know I shouldn't really expect SCSI performance from SATA discs, but this seems a bit much to me (I also have write-caching turned off on my SCSI discs, but I have enabled tagged queueing). I'm still slightly uncomfortable with the idea of software RAID, but it hasn't lost anything yet, in spite of a few "unplanned outages". Chris.
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