From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladimir Milovanovic Subject: Re: XP RAID vs md Date: Fri, 04 Apr 2003 11:21:16 +0200 Sender: linux-raid-owner@vger.kernel.org Message-ID: <3E8D4E8C.7080503@webmail.co.za> References: <3E8AD562.6090707@webmail.co.za> <20030402152731.GE7364@marowsky-bree.de> <3E8D463F.98EFBF1F@llgc.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: To: Illtud Daniel Cc: raid-list List-Id: linux-raid.ids Well Daniel what is your take on this? I am very interested in this since I am working on a project which has to use RAID, and performance is paramount (after reliability of course). I need to make a decision, and I would like very much to stick with md, since it is what I know and am used to. But if one can get huge performance margins using XP, then I am going to have to consider that. Cheers, Vlad. Illtud Daniel wrote: >[posted & mailed] > >Lars Marowsky-Bree wrote: > > > >>>Wow... I hope that one of the maintainers will comment on this, I didn't >>>even know that XP had a sw RAID implementation. Up to 100% more on read >>>and 60% more on write is quite a significant margin. Is there anything >>>in favour of the md driver if this is true? >>> >>> >>I've not really checked these numbers yet, so take the following with a grain >>of salt. >> >> > >Have a look at http://www.hpl.hp.com/techreports/2002/HPL-2002-352.pdf >- that'll tell you were the figures are from - the 100% is worst-case. > > > >>However, with RAID1 for example, I got approximately twice the read speed and >>95% of the write speed (compared to just using a single disk). >> >> > >One thing I forgot to mention in my post is that this is all (AFAICS) >RAID0. > > > >>I have a really hard time imagining a 100% read boost; that would simply >>exceed disk bandwidth, and 60% writes - how should that work? >> >> > >The md driver seriously underperforms at certain request sizes, and >is generally underperforming. The average boost is less, but still about >40-60% read and 30-40% write. XP's RAID0 is better than JBOD above a >certain request size, which is pretty good. > > > >>I'm not claiming md is perfect or the fastest imaginable solution, but it is >>rather close to theoretical disk bandwidth. A two digit percentage performance >>improvement just can't be done. >> >> > >Well, that's why I asked in my original post for people to look at >the report. Is isn't that long and it's pretty clear (although short >on config details). > >-- >Illtud Daniel illtud.daniel@llgc.org.uk >Uwch Ddadansoddwr Systemau Senior Systems Analyst >Llyfrgell Genedlaethol Cymru National Library of Wales >Yn siarad drosof fy hun, nid LlGC - Speaking personally, not for NLW >- >To unsubscribe from this list: send the line "unsubscribe linux-raid" in >the body of a message to majordomo@vger.kernel.org >More majordomo info at http://vger.kernel.org/majordomo-info.html > > >