From owner-freebsd-current Tue Dec 11 14:42: 7 2001 Delivered-To: freebsd-current@freebsd.org Received: from freebie.xs4all.nl (freebie.xs4all.nl [213.84.32.253]) by hub.freebsd.org (Postfix) with ESMTP id ABE9D37B405; Tue, 11 Dec 2001 14:41:57 -0800 (PST) Received: (from wkb@localhost) by freebie.xs4all.nl (8.11.6/8.11.6) id fBBMfqO72106; Tue, 11 Dec 2001 23:41:52 +0100 (CET) (envelope-from wkb) Date: Tue, 11 Dec 2001 23:41:51 +0100 From: Wilko Bulte To: Greg Lehey Cc: Matthew Dillon , Mike Smith , Terry Lambert , Joerg Wunsch , freebsd-current@FreeBSD.org Subject: Re: RAID performance (was: cvs commit: src/sys/kern subr_diskmbr.c) Message-ID: <20011211234151.A72046@freebie.xs4all.nl> References: <200112101754.fBAHsRV01202@mass.dis.org> <200112101813.fBAIDKo47460@apollo.backplane.com> <20011210192251.A65380@freebie.xs4all.nl> <200112101830.fBAIU4w47648@apollo.backplane.com> <20011211110633.M63585@monorchid.lemis.com> <20011211153437.A69755@freebie.xs4all.nl> <20011212090034.C67986@monorchid.lemis.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <20011212090034.C67986@monorchid.lemis.com>; from grog@FreeBSD.org on Wed, Dec 12, 2001 at 09:00:34AM +1030 X-OS: FreeBSD 4.4-STABLE X-PGP: finger wilko@freebsd.org Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Wed, Dec 12, 2001 at 09:00:34AM +1030, Greg Lehey wrote: > On Tuesday, 11 December 2001 at 15:34:37 +0100, Wilko Bulte wrote: > > On Tue, Dec 11, 2001 at 11:06:33AM +1030, Greg Lehey wrote: > >> On Monday, 10 December 2001 at 10:30:04 -0800, Matthew Dillon wrote: > >>> .. > >>> and will go down the drain for reads if you cross a stripe - > >>> something that is quite common I think. > >> > >> I think this is what Mike was referring to when talking about parity > >> calculation. In any case, going across a stripe boundary is not a > >> good idea, though of course it can't be avoided. That's one of the > >> arguments for large stripes. > > > > In a former life I was involved with a HB striping product for SysVr2 > > that had a slightly modified filesystem that 'knew' when it was > > working on a striped disk. And as it know, it avoided posting I/O s > > that crossed stripes. > > So what did it do with user requests which crossed stripes? Memory is dim, but I think the fs code created a second i/o to the driver layer. So the fs never sent out an i/o that the driver layer had to break up. In case of a pre-fetch while reading I think the f/s would just pre-fetch until the stripe border and not bother sending out a second i/o down. In the end all of this benchmarked quite favorably. Note that this was 386/486 era, with the classic SysV filesystem. -- | / o / /_ _ email: wilko@FreeBSD.org |/|/ / / /( (_) Bulte Arnhem, The Netherlands To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message