From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Christensen Subject: Re: RAID-5 streaming read performance Date: Wed, 13 Jul 2005 08:48:02 -0400 Message-ID: <87eka2g9dp.fsf@uwo.ca> References: <874qb14btr.fsf@uwo.ca> <1121220487.5552.34.camel@localhost.localdomain> <87mzorfmdx.fsf@uwo.ca> <1121257494.5504.4.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7BIT Return-path: In-reply-to: <1121257494.5504.4.camel@localhost.localdomain> Sender: linux-raid-owner@vger.kernel.org To: mingz@ele.uri.edu Cc: Linux RAID List-Id: linux-raid.ids Ming Zhang writes: > have u try the parallel write? I haven't tested it as thoroughly, as it brings lvm and the filesystem into the mix. (The disks are in "production" use, and are fairly full, so I can't do writes directly to the disk partitions/raid device.) My preliminary finding is that raid writes are faster than non-raid writes: 49MB/s vs 39MB/s. Still not stellar performance, though. Question for the list: if I'm doing a long sequential write, naively each parity block will get recalculated and rewritten several times, once for each non-parity block in the stripe. Does the write-caching that the kernel does mean that each parity block will only get written once? Dan