Date: Wed, 30 Jan 2002 14:43:26 -0600 From: "Scott Gerhardt" <scott@gerhardt-it.com> To: "Brian T.Schellenberger" <bts@babbleon.org>, "Espen Tagestad" <espen@modula.no>, <questions@FreeBSD.ORG> Subject: RE: Softupdates Message-ID: <KPEMLBLEMPMHGLJOCDEGIEHIDLAA.scott@gerhardt-it.com> In-Reply-To: <20020130191439.323464078@i8k.babbleon.org>
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> > Now it IS a bad idea (even though many people do it without > happening to get > burned) to run with write caching *and* softupdates both on. > In general, > it's a bad isea to run with write caching, period, but > combining it with > softupdates makes things a lot worse, but softupdates without > write caching > is safer than the other way 'round. Of course, turning both > off is safest > and slowest, so pick your poison. I use softupdates on ALL > file systems and > turn off write caching myself. > > (To turn off write-caching, put this in /boot/loader.conf: > > # write cache considered dangerous > hw.ata.wc=0 > ) > > The reason for the general advice to turn it off on / is > because it does > introduce a delay and / is traditionally rather small. The > delay effectively > gives you less space in a file system since freed space may > not be freed yet, > but if you make / larger than usual and turn on softupdates > you'll get the > speed benefit of softupdates and yet won't risk running out > of disk space. > > (It seems an especial shame to turn off softupdates on > whatever file system > contains /tmp since the benefits are larger on a file system > with lots of > writes.) The write caching issue is more of an IDE-ATA issue. As far as I know write caching is not such an issue with the newer SCSI drives that have Tagged Queueing Enabled (see dmesg from one of my systems below). Excerpt from dmesg: da0 at ahc0 bus 0 target 0 lun 0 da0: <IBM-PSG DDYS-T18350M M S9PC> Fixed Direct Access SCSI-3 device da0: 160.000MB/s transfers (80.000MHz, offset 63, 16bit), Tagged Queueing Enabled I could be wrong, so correct me if I am. Regards, - Scott To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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