From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stan Hoeppner Subject: Re: Possible to change chunk size on RAID-1 without re-init or destructive result? Date: Sun, 31 Mar 2013 19:28:43 -0500 Message-ID: <5158D4BB.6070801@hardwarefreak.com> References: <16639206.20.1364400094382.JavaMail.root@zimbra> <51534450.8050905@hardwarefreak.com> <51535252.2080105@hardwarefreak.com> <51536DDD.5010800@hardwarefreak.com> <51585CB9.5020208@hardwarefreak.com> <51587548.3060306@hardwarefreak.com> Reply-To: stan@hardwarefreak.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: Mark Knecht Cc: Roy Sigurd Karlsbakk , Jeff Johnson , Linux-RAID List-Id: linux-raid.ids On 3/31/2013 12:56 PM, Mark Knecht wrote: > On Sun, Mar 31, 2013 at 10:41 AM, Stan Hoeppner wrote: >> On 3/31/2013 12:15 PM, Mark Knecht wrote: > >>> >>> Hopefully that gives you enough info to suggest a direction. >> >> These applications append small data slowly over a long period of time, >> which usually means fragmentation. Thus there's not much to optimize at >> the chunk/stripe level, other than keeping chunk size small to spread >> random reads over all platters. You currently have a 16KB chunk, IIRC, >> which is about as good as you'll get for this workload. Given your >> applications' low write throughput chunk/strip really doesn't matter. >> >> -- >> Stan >> > > OK, I cannot argue with your conclusions and will stick with 16K for now. > > Presumably if any improvement is to be made here its getting > everything onto a single partition instead of multiple RAIDs on the > same drives which then reduces the physical overhead (moving heads to > different partitions) and allows the md software to do the heavy > lifting? Your write IO rate appears to be so low that it really makes no difference. I'd guess you could run all of this from a single fast disk drive (10/15K or SSD) without skipping a beat. -- Stan