From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: Grub-install, superblock corrupted/erased and other animals Date: Wed, 3 Aug 2011 19:20:54 +1000 Message-ID: <20110803192054.6097d2c0@notabene.brown> References: <20110802163907.29fc40b4@notabene.brown> <20110803150108.58f5c70b@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Aaron Scheiner Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On Wed, 3 Aug 2011 10:59:22 +0200 Aaron Scheiner wrote: > mmm, learning experience :P > > The Wikipedia page on grub says : > " > Stage 1 can load Stage 2 directly, but it's normally set up to load > Stage 1.5. GRUB Stage 1.5 is located in the first 30 kilobytes of hard > disk immediately following the MBR and before the first partition. > " > So if both stage 1 and stage 1.5 were written to the drives > approximately 30KBytes would have been overwritten, so 60 sectors? > > Why is the data offset by 256 bytes ? The array was created using a > standard create command (only specifying raid level, devices, chunk > size). The offset is 256 sectors (64K). The data obviously cannot go at the start of the drive as the metadata is there, so it is offset from the start. I leave 64K to allow for various different metadata (bitmap, bad-block log, other ideas I might have one day). NeilBrown