From owner-freebsd-current Mon Dec 10 18:26:13 2001 Delivered-To: freebsd-current@freebsd.org Received: from srv1.cosmo-project.de (srv1.cosmo-project.de [213.83.6.106]) by hub.freebsd.org (Postfix) with ESMTP id 484E037B626; Mon, 10 Dec 2001 18:25:15 -0800 (PST) Received: (from uucp@localhost) by srv1.cosmo-project.de (8.11.0/8.11.0) with UUCP id fBB2PAf62929; Tue, 11 Dec 2001 03:25:10 +0100 (CET) Received: from mail.cicely.de (cicely20.cicely.de [10.1.1.22]) by cicely5.cicely.de (8.12.1/8.12.1) with ESMTP id fBB2PVtx001312; Tue, 11 Dec 2001 03:25:31 +0100 (CET)?g (envelope-from ticso@cicely8.cicely.de) Received: from cicely8.cicely.de (cicely8.cicely.de [10.1.2.10]) by mail.cicely.de (8.11.0/8.11.0) with ESMTP id fBB2PTW05549; Tue, 11 Dec 2001 03:25:29 +0100 (CET) Received: (from ticso@localhost) by cicely8.cicely.de (8.11.6/8.11.6) id fBB2PMV13813; Tue, 11 Dec 2001 03:25:22 +0100 (CET) (envelope-from ticso) Date: Tue, 11 Dec 2001 03:25:21 +0100 From: Bernd Walter To: Matthew Dillon Cc: Wilko Bulte , Mike Smith , Terry Lambert , Joerg Wunsch , freebsd-current@FreeBSD.ORG Subject: Re: cvs commit: src/sys/kern subr_diskmbr.c Message-ID: <20011211032521.H11774@cicely8.cicely.de> References: <200112101754.fBAHsRV01202@mass.dis.org> <200112101813.fBAIDKo47460@apollo.backplane.com> <20011210192251.A65380@freebie.xs4all.nl> <200112101849.fBAInSO47847@apollo.backplane.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200112101849.fBAInSO47847@apollo.backplane.com> User-Agent: Mutt/1.3.23i X-Operating-System: FreeBSD cicely8.cicely.de 5.0-CURRENT i386 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 Mon, Dec 10, 2001 at 10:49:28AM -0800, Matthew Dillon wrote: > > :For RAID3 that is true. For the other ones... > : > :> 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. > : > :-- > :| / o / /_ _ email: wilko@FreeBSD.org > :|/|/ / / /( (_) Bulte Arnhem, The Netherlands > > Well, for reads a non-stripe-crossing op would still work reasonably > well. But for writes less then full-stripe operations without > spindle sync are going to be terrible due to the read-before-write > requirement (to calculate parity). The disk cache is useless in that > case. Modern disks do prereads and writes are streamed by tagged command queueing which invalidates this for linear access. For non linear access the syncronisation is shadowed partly by different seek times and different load on the spindles. The chance that the data and parity spindle have the heads on the same track is absolutely small for random access. With 15000 upm drives the maximum rotational delay is 4ms and the average is 2ms which gives you an maximum of only 1ms to gain under ideal conditions - which we don't have as I stated above. -- B.Walter COSMO-Project http://www.cosmo-project.de ticso@cicely.de Usergroup info@cosmo-project.de To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message