From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Robinson Subject: Re: First raid1 sector gets zeroed at first reboot Date: Wed, 17 Aug 2011 15:34:46 +0100 Message-ID: <4E4BD186.4070604@anonymous.org.uk> References: <4E4AABF6.2070800@shiftmail.org> <4E4BC586.10109@anonymous.org.uk> <4E4BC96D.1020802@shiftmail.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4E4BC96D.1020802@shiftmail.org> Sender: linux-raid-owner@vger.kernel.org To: Asdo Cc: linux-raid List-Id: linux-raid.ids On 17/08/2011 15:00, Asdo wrote: > On 08/17/11 15:43, John Robinson wrote: >> >> The first sector of a md RAID with metadata 1.0 is in its data area, >> so there's no way md is writing to this area itself, it's almost >> certainly the filesystem that's writing it. >> >> I think installing grub on a md partition is a bad idea. You can use >> metadata 1.2 to have the first 4K left free, but grub may write its >> stage 1.5 code to the first 31.5K of a device (whole drive or partition). >> > > No you are confusing it with metadata 1.1 . > Metadata 1.0 has the data at the end like 0.9 . No I'm afraid it's you that's confused. Metadata 1.0 has the *metadata* at the end, like 0.9, so it has the data i.e. filesystem area at the beginning. Take a look with mdadm -D, the data offset is zero. This is why partitions with 0.9 or 1.0 metadata in RAID-1 can be used individually to boot from because the partitions look identical to ones that just have filesystems on them. Cheers, John.