From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: How to avoid complete rebuild of RAID 6 array (6/8 active devices) Date: Fri, 27 Jun 2008 20:40:14 +1000 Message-ID: <18532.50062.63173.620773@notabene.brown> References: <41931C59-9A91-47A6-A81C-EC14001DA95B@gmail.com> <20080625161357.GH23944@skl-net.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: message from Andre Noll on Wednesday June 25 Sender: linux-raid-owner@vger.kernel.org To: Andre Noll Cc: Dave Moon , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Wednesday June 25, maan@systemlinux.org wrote: > On 15:37, Dave Moon wrote: > > > 1. If mdadm encounters a bit error during a RAID 6 rebuild, will it > > just give up on that particular file and move on to recover other data > > on the array? Or will it trash the entire array? > > The kernel will stop the array and give up. Not quite. It will stop the recovery. It won't stop the whole array though (I think...). > > > 2. Is it possible to cheat mdadm by somehow replacing the new "raid > > metadata" on the 6 drives with the old data on the 2 drives? Will it > > make mdadm think the array is clean, consistent and nothing ever > > happened? > > > Please do note that I did not write ANY new data onto the RAID 6 array > > from the time it was degraded until the time I brought it down with (-- > > stop). > > Use --force, Luke. Man mdadm(8): > > -f, --force Assemble the array even if some superblocks > appear out-of-date --force only updates enough superblocks to assemble a working array. For raid6, that mean n-2 drives. As there are n-2 drive, it won't try any harder. You best bet is to recreate the array with --assume-clean. Providing you have the chunksize, order of devices, etc the same, you should get your array back. NeilBrown