From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: limits on raid Date: Sun, 17 Jun 2007 13:16:30 -0400 Message-ID: <46756C6E.1070106@tmr.com> References: <18034.479.256870.600360@notabene.brown> <18034.3676.477575.490448@notabene.brown> <20070616020320.GB2002@animx.eu.org> <18035.23867.576212.859440@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: david@lang.hm Cc: Neil Brown , Wakko Warner , linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org List-Id: linux-raid.ids david@lang.hm wrote: > On Sat, 16 Jun 2007, Neil Brown wrote: > >> It would be possible to have a 'this is not initialised' flag on the >> array, and if that is not set, always do a reconstruct-write rather >> than a read-modify-write. But the first time you have an unclean >> shutdown you are going to resync all the parity anyway (unless you >> have a bitmap....) so you may as well resync at the start. >> >> And why is it such a big deal anyway? The initial resync doesn't stop >> you from using the array. I guess if you wanted to put an array into >> production instantly and couldn't afford any slowdown due to resync, >> then you might want to skip the initial resync.... but is that really >> likely? > > in my case it takes 2+ days to resync the array before I can do any > performance testing with it. for some reason it's only doing the > rebuild at ~5M/sec (even though I've increased the min and max rebuild > speeds and a dd to the array seems to be ~44M/sec, even during the > rebuild) > > I want to test several configurations, from a 45 disk raid6 to a 45 > disk raid0. at 2-3 days per test (or longer, depending on the tests) > this becomes a very slow process. > I've been doing stuff like this, but I just build the array on a partition per drive so the init is livable. For the stuff I'm doing a total of 500-100GB is ample to do performance testing. > also, when a rebuild is slow enough (and has enough of a performance > impact) it's not uncommon to want to operate in degraded mode just > long enought oget to a maintinance window and then recreate the array > and reload from backup. -- bill davidsen CTO TMR Associates, Inc Doing interesting things with small computers since 1979