From mboxrd@z Thu Jan 1 00:00:00 1970 From: Justin Piszcz Subject: Re: AWFUL reshape speed with raid5. Date: Mon, 28 Jul 2008 15:43:32 -0400 (EDT) Message-ID: References: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Jon Nelson Cc: LinuxRaid List-Id: linux-raid.ids There once was a bug in an earlier kernel, in which the min_speed is what the rebuild ran at if you had a specific chunk size, have you tried to echo 30000 > to min_speed? Does it increase it to 30mb/s for the rebuild? On Mon, 28 Jul 2008, Jon Nelson wrote: > Some more data points, observations, and questions. > > For each test, I'd --create the array, drop the caches, --grow, and > then watch vmstat and also record the time between > > kernel: md: resuming resync of md99 from checkpoint. > and > kernel: md: md99: resync done. > > I found two things: > > 1. metadata version matters. Why? > 2. VERY LITTLE I/O takes place (between 0 and 100KB/s, typically no > I/O at all) according to vmstat. Why? If it takes 1m34s to "grow" the > array, but no I/O is taking place, then what is actually taking so > long? > 3. I removed the bitmap for these tests. Having a bitmap meant that > the overall speed was REALLY HORRIBLE. > > The results: > > metadata: time taken > > 0.9: 27s > 1.0: 27s > 1.1: 37s > 1.2: 1m34s > > Questions (repeated): > > 1. Why does the metadata version matter so much? > 2. If no I/O is taking place, why does it take so long? [ NOTE: I/O > must be taking place but why doesn't vmstat show it? ] > > -- > Jon >