From owner-freebsd-current Tue Dec 11 6:34:44 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 4D5C937B416; Tue, 11 Dec 2001 06:34:39 -0800 (PST) Received: (from wkb@localhost) by freebie.xs4all.nl (8.11.6/8.11.6) id fBBEYbS69823; Tue, 11 Dec 2001 15:34:37 +0100 (CET) (envelope-from wkb) Date: Tue, 11 Dec 2001 15:34:37 +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: <20011211153437.A69755@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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <20011211110633.M63585@monorchid.lemis.com>; from grog@FreeBSD.org on Tue, Dec 11, 2001 at 11:06:33AM +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 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: > > > >>> performance without it - for reading OR writing. It doesn't matter > >>> so much for RAID{1,10}, but it matters a whole lot for something like > >>> RAID-5 where the difference between a spindle-synced read or write > >>> and a non-spindle-synched read or write can be upwards of 35%. > >> > >> If you have RAID5 with I/O sizes that result in full-stripe operations. > > > > Well, 'more then one disk' operations anyway, for random-I/O. Caching > > takes care of sequential I/O reasonably well but random-I/O goes down > > the drain for writes if you aren't spindle synced, no matter what > > the stripe size, > > Can you explain this? I don't see it. In FreeBSD, just about all I/O > goes to buffer cache. > > > 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. W/ -- | / 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