From owner-freebsd-scsi Sat Oct 3 19:17:39 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id TAA12598 for freebsd-scsi-outgoing; Sat, 3 Oct 1998 19:17:39 -0700 (PDT) (envelope-from owner-freebsd-scsi@FreeBSD.ORG) Received: from smtp02.primenet.com (smtp02.primenet.com [206.165.6.132]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id TAA12494; Sat, 3 Oct 1998 19:16:55 -0700 (PDT) (envelope-from tlambert@usr06.primenet.com) Received: (from daemon@localhost) by smtp02.primenet.com (8.8.8/8.8.8) id TAA15523; Sat, 3 Oct 1998 19:16:30 -0700 (MST) Received: from usr06.primenet.com(206.165.6.206) via SMTP by smtp02.primenet.com, id smtpd015497; Sat Oct 3 19:16:20 1998 Received: (from tlambert@localhost) by usr06.primenet.com (8.8.5/8.8.5) id TAA19402; Sat, 3 Oct 1998 19:16:15 -0700 (MST) From: Terry Lambert Message-Id: <199810040216.TAA19402@usr06.primenet.com> Subject: Re: filesystem safety and SCSI disk write caching To: bde@zeta.org.au (Bruce Evans) Date: Sun, 4 Oct 1998 02:16:15 +0000 (GMT) Cc: bde@zeta.org.au, tlambert@primenet.com, Don.Lewis@tsc.tdk.com, freebsd-fs@FreeBSD.ORG, freebsd-scsi@FreeBSD.ORG, gibbs@plutotech.com In-Reply-To: <199810040137.LAA14507@godzilla.zeta.org.au> from "Bruce Evans" at Oct 4, 98 11:37:22 am X-Mailer: ELM [version 2.4 PL25] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-scsi@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org > >> I think it can be interpreted as showing that the performance hit is > >> very large. `make world' is mostly cpu-bound, and most of it's i/o's > >> are reads (60% here). I guess it spends less than 5 minutes of its time > >> writing (27000 block output operations here). An increase of 5 minutes > >> is very large. > > > >This is without "noatime". > > Actually, 27000 is with "noatime" on all file systems, and with "async" > on all file systems that were written to by my `make world' (/tmp, /var/tmp, > MAKEOBJDIRPREFIX = /c/obj and DESTDIR = /c/root). Even better. We are talking an increase of one hour, 30, to one hour, 35 in trade for soft update without atime and without SCSI write caching enabled. This is from 90 to 95 minutes, or 95/90 = 1.0555. This is a difference of 5.6% to go from zero reliability to 100% reliability, barring hardware failure. In my book, this is overhead *well spent*. I can post (once again) the results of a Novell study on server usage patterns. The 30,000 foot view for a typical server breaks down to: 75% reads 15% writes 8% directory search operations 2% other Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message