From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: RAID1 and load-balancing during read Date: Tue, 11 Sep 2007 16:11:40 +0200 Message-ID: <18150.41500.375266.283053@notabene.brown> References: <200709102229.30655.jimis@gmx.net> <20070910193530.GB2597@teal.hq.k1024.org> <200709102251.37976.jimis@gmx.net> <20070911034417.GA20596@teal.hq.k1024.org> <877imxibj2.fsf@informatik.uni-tuebingen.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: message from Goswin von Brederlow on Tuesday September 11 Sender: linux-raid-owner@vger.kernel.org To: Goswin von Brederlow Cc: Dimitrios Apostolou , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Tuesday September 11, brederlo@informatik.uni-tuebingen.de wrote: > > I found that near copies behave like raid1, offset copies are slower > in both reading and writing (beats me why) and far copies are slightly > faster than near copies in write and twice as fast in read. All for > sequential read/write. For random writes far copies should be slower > to write. I would expect read performance on an 'offset' layout to be significantly affected by the chunk size. You probably want the chunk size to be about 4 times the cylinder size. The ideal would be exactly the cylinder size, and exactly aligned to cylinders. But as cylinder sizes change across the device, this is not possible. Unfortunately I don't know how big cylinders are. I suspect if you hunt through the docs for the device you might find out. NeilBrown