Date: Thu, 30 Aug 2001 21:29:41 -0500 From: Mike Meyer <mwm@mired.org> To: jim@nasby.net Cc: Mike Meyer <mwm@mired.org>, Trevin Chow <tmchow@sfu.ca>, questions@freebsd.org Subject: Re: SCSI write caching (was: Re: Performance tuning and adding RAM) Message-ID: <15246.63125.744922.260778@guru.mired.org> In-Reply-To: <20010830202206.R63459@enteract.com> References: <15245.36122.131328.798913@guru.mired.org> <20010829215734.F79672-100000@benny.geektank.org> <15245.52453.614096.245669@guru.mired.org> <20010830202206.R63459@enteract.com>
next in thread | previous in thread | raw e-mail | index | archive | help
Jim C. Nasby <jim@nasby.net> types: > On Thu, Aug 30, 2001 at 12:19:33AM -0500, Mike Meyer wrote: > > If you are using SCSI disks, you can use the camcontrol modepage > > command to check and disable it. It's the WCE value on page 8; use > > "camcontrol modepage daX -m 8 -e" to start an editor, change the 1 to > > a 0, and then exit. > Is this also necessary with SCSI drives? I was under the impression that they > weren't susceptible to this problem... Thank you for catching this. It used to be necessary for SCSI drives, but that's no longer universally true. SCSI supports a feature called tagged queuing, which means that the system can reliably determine when blocks have been written to disk even if write caching is enabled. If the driver you are using supports tagged queueing, you can enable the write cache on the drives attached to it. I believe all currently supported drivers support tagged queuing if the controller does. The manual page for the driver should say whether or not it supports tagged queueing. To answer the obvious followup, IDE drives that do tagged queuing are starting to appear, and the ata driver supports them. See the tuning and ata man pages for more information. <mike -- Mike Meyer <mwm@mired.org> http://www.mired.org/home/mwm/ Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?15246.63125.744922.260778>