From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Tokarev Subject: Re: Linux RAID Partition Offset 63 cylinders / 30% performance hit? Date: Sun, 30 Dec 2007 04:33:09 +0300 Message-ID: <4776F555.7040607@msgid.tls.msk.ru> References: <20071219215948.GA7129@cthulhu.home.robinhill.me.uk> <477154C1.6000503@tmr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Justin Piszcz Cc: dean gaudet , Bill Davidsen , linux-raid@vger.kernel.org, Alan Piszcz List-Id: linux-raid.ids Justin Piszcz wrote: [] > Good to know/have it confirmed by someone else, the alignment does not > matter with Linux/SW RAID. Alignment matters when one partitions Linux/SW raid array. If the inside partitions will not be aligned on a stripe boundary, esp. in the worst case when the filesystem blocks cross the stripe boundary (wonder if it's ever possible... and I think it is, if a partition starts at some odd 512 bytes boundary, and filesystem block size is 4Kb, there's just no chance for an inside filesystem to do full-stripe writes, ever, so (modulo stripe cache size) all writes will go read-modify-write or similar way. And that's what the original article is about, by the way. It just happens that hardware raid array is more often split into partitions (using native tools) than linux software raid arrays. And that's what has been pointed out in this thread, as well... ;) /mjt