Date: Thu, 11 Feb 1999 21:55:07 +0100 From: Andreas Klemm <andreas@klemm.gtn.com> To: "Kenneth D. Merry" <ken@plutotech.com> Cc: Andreas Klemm <andreas@klemm.gtn.com>, gibbs@pluto.plutotech.com, scsi@FreeBSD.ORG, se@FreeBSD.ORG Subject: Re: 2.2.7/3.0-STABLE: tagged command queueing && poor write performance Message-ID: <19990211215507.B24839@titan.klemm.gtn.com> In-Reply-To: <199902112033.NAA30231@panzer.plutotech.com>; from Kenneth D. Merry on Thu, Feb 11, 1999 at 01:33:49PM -0700 References: <19990211203455.A19293@titan.klemm.gtn.com> <199902112033.NAA30231@panzer.plutotech.com>
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Hi Kenneth, first of all, thanks for your quick response. On Thu, Feb 11, 1999 at 01:33:49PM -0700, Kenneth D. Merry wrote: > > > > Other observations are, that if tagged command queuing is active > > and I start bonnie, I nearly can't login to a second vty. And > > commands are delayed for about 10-15 seconds !!! > > That is, I think, more of a problem with CAM's queueing algorithms. Justin > has talked of tuning them, or perhaps the way the upper layer code queues > things. I'll see if this effect goes away with turning off the disks cache... > You can do it in cam_xpt.c. Thanks, already found it. When asking this, I looked into cam/scsi and disn't find entries for that. Found it later one dir above. > The solution is to disable write caching for that disk, and see if that > helps you any. To disable write caching, edit mode page 8: > > camcontrol modepage -v -n da -u 0 -m 0x8 -e > > Change the "WCE" bit from 1 to 0, and save it. Ok, thanks, will try it. > In my experience, this will definitely increase the throughput you get to > the disk for sequential writes. For many of my machines, though, I leave > write caching turned on, since I think that in the general case write > caching on the disk will help random I/O performance. > > I am assuming here that your disk has write caching turned on. Many disk > drive vendors ship with it turned on. (Seagate does, I think. IBM may > not, but I think Quantum does.) If your disk doesn't have write caching > enabled, then you've probably got some other problem. I already looked for this. It's true, the disk has write cache on. I'll try disabling the cache ! Best regards Andreas /// -- Andreas Klemm http://www.FreeBSD.ORG/~andreas What gives you 90% more speed, for example, in kernel compilation ? http://www.FreeBSD.ORG/~fsmp/SMP/akgraph-a/graph1.html "NT = Not Today" (Maggie Biggs) ``powered by FreeBSD SMP'' To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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