From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hubert Verstraete Subject: Re: RAID5 losing initial synchronization on restart when one disk is spare Date: Thu, 12 Jun 2008 15:05:57 +0200 Message-ID: <48511F35.90701@free.fr> References: <48466AD9.5@free.fr> <484E6C3F.4090204@free.fr> <484FE4C4.5020100@free.fr> <18512.25101.824044.407896@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: <18512.25101.824044.407896@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: > On Wednesday June 11, hubskml@free.fr wrote: >> By the way and FYI, with my configuration, all disks on the same >> controller, internal bitmap, v1 superblock, ... the initial RAID-5 >> synchronization duration is the same whether I'm using the option >> --force or not. > > For this to be a valid test, you need to fill one drive up with > garbage to ensure that a resync is no a no-op. > > If you don't use the "--force" option, then the recovery process will > read from N-1 drives and write to 1 drive, all completely sequentially > so it will go at a predictable speed. > > When you use "--force" it will read from N drive and check parity. > When it finds an error it will re-write that parity block. > So if the parity blocks happen to be all correct (as probably was the > case in your experiment), it will run nice and fast. If the parity > blocks happen to all be wrong (as is likely when first creating an > array on drives that weren't an array before) it will be much slower. I've just filled all the drives with /dev/zero and am currently building a new array. Is this a valid test or should I fill the drives with /dev/random ? Hubert