From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Greg Cormier" Subject: Re: Superblocks Date: Tue, 30 Oct 2007 12:06:38 -0400 Message-ID: <29a863790710300906w497c0f35yb90c36dadbd2c5e7@mail.gmail.com> References: <29a863790710260943o7623212esce30325be4610dea@mail.gmail.com> <18214.45758.794247.651163@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <18214.45758.794247.651163@notabene.brown> Content-Disposition: inline Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Which is the default type of superblock? 0.90 or 1.0? On 10/30/07, Neil Brown wrote: > On Friday October 26, gcormier@gmail.com wrote: > > Can someone help me understand superblocks and MD a little bit? > > > > I've got a raid5 array with 3 disks - sdb1, sdc1, sdd1. > > > > --examine on these 3 drives shows correct information. > > > > > > However, if I also examine the raw disk devices, sdb and sdd, they > > also appear to have superblocks with some semi valid looking > > information. sdc has no superblock. > > If a partition starts a multiple of 64K from the start of the device, > and ends with about 64K of the end of the device, then a superblock on > the partition will also look like a superblock on the whole device. > This is one of the shortcomings of v0.90 superblocks. v1.0 doesn't > have this problem. > > > > > How can I clear these? If I unmount my raid, stop md0, it won't clear it. > > mdadm --zero-superblock device name > > is the best way to remove an unwanted superblock. Ofcourse in the > above described case, removing the unwanted superblock will remove the > wanted one aswell. > > > > > > [root@zeus ~]# mdadm --zero-superblock /dev/hdd > > mdadm: Couldn't open /dev/hdd for write - not zeroing > > As I think someone else pointed out "/dev/hdd" is not "/dev/sdd". > > NeilBrown >