From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Software RAID 6 initial sync very slow Date: Tue, 03 Jun 2008 15:47:52 -0400 Message-ID: <48459FE8.6080604@tmr.com> References: <8CA91F18992AC9E-1724-EAF@webmail-ne13.sysops.aol.com> <4843E8FD.8000601@tmr.com> <8CA92FCA38FE330-1A8-162F@webmail-nb02.sysops.aol.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <8CA92FCA38FE330-1A8-162F@webmail-nb02.sysops.aol.com> Sender: linux-raid-owner@vger.kernel.org To: thomas62186218@aol.com Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids thomas62186218@aol.com wrote: > Thank you Bill and Richard for your responses. > > In sync_speed_max, I had already set it to 250000 (250MB/sec). For > sync_speed_min, I have 249900 set. My rational behind doing this was > to "force" it to go as fast as it can. Any problem with this? > Other than possibly totally killing your response if you use some other raid levels, no. I usually set the min speed to something I can tolerate in the background, and still have a useful system. > However, adjusting stripe_cache_size did improve performance. It was > 256 at first, and my sync rate was 28MB/sec. When I increased it to > 4096, my sync rate jumped to 38MB/sec. Then I increased it to 16384, > and it jumped again to 40MB/sec. Increasing stripe_cache_size above > that did not seem to have any effect. > You definitely hit diminishing returns on cache_size. There are people on this list who swear by 32k or 64k, but even when I can spare the memory I don't see any benefit to looking for that last tiny gain. > My question then is, how do I set the stripe_cache_size at the time of > md creation? I would rather set it then, as opposed to having to echo > stripe_cache_size variable with a new setting. In other words, where > is this default value of 256 coming from? Thanks all!! rc.local is my usual choice for things like that, and if you want to really spend a lot of time chasing performance, be aware that you can use blockdev to play with readahead on the devince and filesystem, and generally spend days trying to create a test which will show benefits in a statistically valid manner. Add chunk size and knock yourself out. I am convinced that the answer to better performance is "it depends," so just boosting readahead and cache_size a bit usually gets 80-90% of anything you can get with tons of playing. -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark