From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: Superblocks Date: Tue, 30 Oct 2007 15:27:42 +1100 Message-ID: <18214.45758.794247.651163@notabene.brown> References: <29a863790710260943o7623212esce30325be4610dea@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: message from Greg Cormier on Friday October 26 Sender: linux-raid-owner@vger.kernel.org To: Greg Cormier Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids 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