From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Greaves Subject: Re: RAID-5 streaming read performance Date: Wed, 13 Jul 2005 22:50:11 +0100 Message-ID: <42D58C93.3070602@dgreaves.com> 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> <42D5573A.6090801@dgreaves.com> <1121278451.5504.79.camel@localhost.localdomain> <42D58541.7000702@dgreaves.com> <1121291045.5504.108.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1121291045.5504.108.camel@localhost.localdomain> Sender: linux-raid-owner@vger.kernel.org To: mingz@ele.uri.edu Cc: Dan Christensen , Linux RAID List-Id: linux-raid.ids Ming Zhang wrote: >On Wed, 2005-07-13 at 22:18 +0100, David Greaves wrote: > > >>Ming Zhang wrote: >> >> >> >>>>component partitions, e.g. /dev/sda7: 39MB/s >>>>raid device /dev/md2: 31MB/s >>>>lvm device /dev/main/media: 53MB/s >>>> >>>>(oldish system - but note that lvm device is *much* faster) >>>> >>>> >>>> >>>> >>>this is so interesting to see! seems that some read ahead parameters >>>have negative impact. >>> >>> >>> >>> >>I guess each raw device does some readahead, then the md0 does some >>readahead and then the lvm does some readahead. Theoretically the md0 >>and lvm should overlap - but I guess that much of the raw device level >>readahead is discarded. >> >>David >> >> >> >for a streaming read, what you readahead now will always be used exact >once in near future. at least i think raw device readahead can be turned >on at the same time with one of OS components, raid or lvm, readahead >being turned on. but in your case, u get best result when turn only one >on. > >ming > > > > > I doubt it's just me - what results do others get with that script? David --