From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Rabbitson Subject: Re: Raid1 replaced with raid10? Date: Mon, 07 May 2007 09:02:51 +0200 Message-ID: <463ECF1B.7000007@rabbit.us> References: <45FF1BDF.6060304@rabbit.us> <463B2D15.7020305@rabbit.us> <463B4C4F.9030504@tmr.com> <17982.42974.461499.127486@notabene.brown> <463ECBF5.7030206@rabbit.us> <17982.52772.893500.146509@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <17982.52772.893500.146509@notabene.brown> Sender: linux-raid-owner@vger.kernel.org Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: > On Monday May 7, rabbit@rabbit.us wrote: >> Neil Brown wrote: >>> On Friday May 4, davidsen@tmr.com wrote: >>>> Peter Rabbitson wrote: >>>>> Hi, >>>>> >>>>> I asked this question back in march but received no answers, so here it >>>>> goes again. Is it safe to replace raid1 with raid10 where the amount of >>>>> disks is equal to the amount of far/near/offset copies? I understand it >>>>> has the downside of not being a bit-by-bit mirror of a plain filesystem. >>>>> Are there any other caveats? >>>>> >>> To answer the original question, I assume you mean "replace" as in >>> "backup, create new array, then restore". >>> You will get different performance characteristics. Whether they >>> better suit your needs or not will depend largely on your needs. >> Hi Neil, >> Yes I meant take an existing 2 drive raid1 array (non bootable data) and >> put a raid10 array in its place. All my testing indicates that I get the >> same write performance but nearly double the read speed (due to >> interleaving I guess). It seemed to good to be true, thus I am asking >> the question. Could you elaborate on your last sentence? Are there >> downsides I could not think of? Thank you! > > I would have thought that you need "far" or "offset" to improve read > performance, and they tend to hurt write performance (though I haven't > really measured "offset" much). > > What layout are you using? > Correct, I am using 'far' layout. The interleaving of the 'offset' layout does not work too good for sequential reads, but far really shines. Yes write performance is hurt by about 10%. Compared to 190% gain in reads I can live with it.