From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nix Subject: Re: only 4 spares and no access to my data Date: Wed, 19 Jul 2006 00:44:31 +0100 Message-ID: <87ac76bhr4.fsf@hades.wkstn.nix> References: <62b0912f0607091223y3d0a1ab5xbc5fb01ce2a74f9e@mail.gmail.com> <44B213CD.5010907@idgmail.se> <17596.17567.790363.193434@cse.unsw.edu.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: <17596.17567.790363.193434@cse.unsw.edu.au> (Neil Brown's message of "18 Jul 2006 03:18:07 +0100") Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Henrik Holst , Karl Voit , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 18 Jul 2006, Neil Brown moaned: > The superblock locations for sda and sda1 can only be 'one and the > same' if sda1 is at an offset in sda which is a multiple of 64K, and > if sda1 ends near the end of sda. This certainly can happen, but it > is by no means certain. > > For this reason, version-1 superblocks record the offset of the > superblock in the device so that if a superblock is written to sda1 > and then read from sda, it will look wrong (wrong offset) and so will > be ignored (no valid superblock here). One case where this can happen is Sun slices (and I think BSD disklabels too), where /dev/sda and /dev/sda1 start at the *same place*. (This causes amusing problems with LVM vgscan unless the raw devices are excluded, too.) -- `We're sysadmins. We deal with the inconceivable so often I can clearly see the need to define levels of inconceivability.' --- Rik Steenwinkel