From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: AWFUL reshape speed with raid5. Date: Wed, 30 Jul 2008 12:23:20 -0400 Message-ID: <48909578.9020307@tmr.com> References: 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: Jon Nelson Cc: Justin Piszcz , LinuxRaid List-Id: linux-raid.ids Jon Nelson wrote: > 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? > I have no idea. > 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? ] > vmstat doesn't tell you enough, you need a tool to show per-device and per-partition io, which will give you what you need. I can't put a finger on the one I wrote, but there are others. -- 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