From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mario 'BitKoenig' Holbe Subject: Re: paralellism of device use in md Date: Thu, 19 Jan 2006 12:30:47 +0100 Message-ID: References: <20060117120927.GU7017@strugglers.net> <43CD8A73.90703@nsr500.net> Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Francois Barre wrote: > 2006/1/18, Mario 'BitKoenig' Holbe : >> Mario 'BitKoenig' Holbe wrote: >> Perhaps using some big (virtual) chunk size could do the trick? What > 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... Yes, this would be the consequence. However, this would probably not be a big issue, since a) the current default read-ahead for RAID1 is 1024 (in 512-byte sectors) anyways. Furthermore, in the hardware-RAID sector b) at least the 3ware support recommends huge read-aheads for speeding up their RAID1s, too... afaik they recommend: vm.{min,max}-readahead=512 blockdev --setra 6144 /dev/... which is far more than 1M. I don't know why they do so but I could imagine they also use some strategy similar to the one I suggested. regards Mario -- Ho ho ho! I am Santa Claus of Borg. Nice assimilation all together!