From mboxrd@z Thu Jan 1 00:00:00 1970 From: Francois Barre Subject: Re: paralellism of device use in md Date: Wed, 18 Jan 2006 18:55:04 +0100 Message-ID: References: <20060117120927.GU7017@strugglers.net> <43CD8A73.90703@nsr500.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Return-path: In-Reply-To: Content-Disposition: inline Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids 2006/1/18, Mario 'BitKoenig' Holbe : > Mario 'BitKoenig' Holbe wrote: > > scheduled read-requests. Would it probably make sense to split one > > single read over all mirrors that are currently idle? > > A I got it from the other thread - seek times :) > Perhaps using some big (virtual) chunk size could do the trick? What > about using chunks that big that seeking is faster than data-transfer... > assuming a data rate of 50MB/s and 9ms average seek time would result in > at least 500kB chunks, 14ms average seek time would result in at least > 750kB chunks. > However, since the blocks being read are most likely somewhat close > together, it's not a typical average seek, so probably smaller chunks > would also be possible. > > > regards > Mario Stop me if I'm wrong, but this is called... huge readahead. Instead of reading 32k on drive0 then 32k on drive1, you read continuous 512k from drive0 (16*32k) and 512k from drive1, resulting in a 1M read. Maybe for a single 4k page... So my additionnal question to this would be : how well does md fit with linux's/fs readahead policies ?