From mboxrd@z Thu Jan 1 00:00:00 1970 From: Goswin von Brederlow Subject: Re: partitioned raid 5 and proper partition alignment Date: Sun, 09 Aug 2009 00:21:35 +0200 Message-ID: <87ws5egd5c.fsf@frosties.localdomain> References: <200908080812.45509.ml_linux_raid@mortal-soul.de> <87skg2vius.fsf@frosties.localdomain> <200908081309.59049.ml_linux_raid@mortal-soul.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: <200908081309.59049.ml_linux_raid@mortal-soul.de> (Matthias Dahl's message of "Sat, 8 Aug 2009 13:09:59 +0200") Sender: linux-raid-owner@vger.kernel.org To: Matthias Dahl Cc: Goswin von Brederlow , linux-raid@vger.kernel.org List-Id: linux-raid.ids Matthias Dahl writes: > Hi. > > On Saturday 08 August 2009 09:56:59 you wrote: > >> But each stripe only holds 128k of data. You have to align to that. > > I beg to differ. There are two data chunks and one parity chunk, thus a whole > stripe is 192k long if you've a 64k chunk size. If you align to 128k and you > put e.g. ext4 on it with the correct fs stride and stripe-width settings, > you'll probably end up with worse performance since you start in the middle of > a stripe even though properly aligned to a chunk boundary. Or am I totally on > the wrong track here...?! Yes you are. The filesystem will never ever see the parity block of a stripe. It only ever sees the 128k data. Writing 128k data will write a full stripe of 192k to disk. MfG Goswin