From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dominic Raferd Subject: Re: SSD + Rust as raid1 Date: Fri, 31 May 2013 09:52:49 +0100 Message-ID: <51A864E1.9070903@timedicer.co.uk> References: <51A7C36F.4030605@timedicer.co.uk> <20130531133018.77cd9285@natsu> <51A85574.8080709@timedicer.co.uk> <20130531135434.5b6bdddb@natsu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130531135434.5b6bdddb@natsu> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 31/05/2013 08:54, Roman Mamedov wrote: > On Fri, 31 May 2013 08:47:00 +0100 > Dominic Raferd wrote: > >> This is my idea too (see my OP), but I am concerned about optimisation >> (--write-behind, --bitmap and --bitmap-chunk settings) especially for >> writes. >> --write-behind=16384 > I think this will not work, you will have to use 16383. Oh, OK, so 16383 is the maximum then? >> --bitmap=/mnt/sda1/write-intent-bitmap.file > Save yourself lots of maintenance headache, just use --bitmap=internal > >> --bitmap-chunk=256M > Looks OK. > Thanks Roman, but the problem with using --bitmap=internal is that, as Neil Brown posted here on another topic a while ago, this requires a synch write to both devices, and the use-case for which write-behind was developed involved an external bitmap. Hence my plan to use external bitmap file on a fast (SSD-based) separate partition - minimises any slow-down caused by having to maintain the write-intent bitmap file.