From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ming Zhang Subject: Re: RAID-5 streaming read performance Date: Wed, 13 Jul 2005 21:25:31 -0400 Message-ID: <1121304331.5504.162.camel@localhost.localdomain> References: <874qb14btr.fsf@uwo.ca> <1121220487.5552.34.camel@localhost.localdomain> <87mzorfmdx.fsf@uwo.ca> <1121257494.5504.4.camel@localhost.localdomain> <87eka2g9dp.fsf@uwo.ca> <1121259126.5504.14.camel@localhost.localdomain> <87vf3eeqe2.fsf@uwo.ca> <1121264997.5504.29.camel@localhost.localdomain> <87r7e2egjk.fsf@uwo.ca> <17109.38909.400379.597785@cse.unsw.edu.au> <1121299773.5504.151.camel@localhost.localdomain> <17109.48385.906137.789190@cse.unsw.edu.au> Reply-To: mingz@ele.uri.edu Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <17109.48385.906137.789190@cse.unsw.edu.au> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Dan Christensen , Linux RAID List-Id: linux-raid.ids On Thu, 2005-07-14 at 11:16 +1000, Neil Brown wrote: > On Wednesday July 13, mingz@ele.uri.edu wrote: > > On Thu, 2005-07-14 at 08:38 +1000, Neil Brown wrote: > > > On Wednesday July 13, jdc@uwo.ca wrote: > > > > Here's a question for people running software raid-5: do you get > > > > significantly better read speed from a raid-5 device than from it's > > > > component partitions/hard drives, using the simple dd test I did? > > > > > > SCSI-160 bus, using just 4 of the 15000rpm drives: > > > > > > each drive by itself delivers about 67M/s > > > Three drives in parallel deliver 40M/s each, total of 120M/s > > > 4 give 30M/s each or a total of 120M/s > > > > > > raid5 over 4 drives delivers 132M/s > > why here a 132MB/s instead of 120MB/s (3 * 40MB/s) as u mentioned? any > > factor lead to this increase? > > > > > > I did another test over 10 times the amount of data, and for 34M/s for > 4 concurrent individual drives, which multiplies out to 136M/s. The > same amount of data of the raid5 gives 137M/s, so I think it was just > experimental error. ic. thanks for explanation. yes, agree. it seems that u can get a near linear performance with decent SCSI HW while what we can get from SATA is not good. :P Ming > > NeilBrown