From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: How to avoid complete rebuild of RAID 6 array (6/8 active devices) Date: Sun, 29 Jun 2008 17:58:30 -0400 Message-ID: <48680586.609@tmr.com> References: <41931C59-9A91-47A6-A81C-EC14001DA95B@gmail.com> <20080625161357.GH23944@skl-net.de> <18532.50062.63173.620773@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <18532.50062.63173.620773@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Andre Noll , Dave Moon , linux-raid@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: > 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 appear out-of-date 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. > Then what? What's going to happen when he does a check? Of course build an array out of drives so unstable that you can't safelt *run* a check is another topic. -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark