From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Bucksch Subject: Re: Use RAID-6! Date: Wed, 17 Apr 2013 13:13:28 +0200 Message-ID: <516E83D8.2070908@bucksch.org> References: <15345091.8.1366130671716.JavaMail.root@zimbra> <516DABF2.5050409@tigertech.com> <516DAF21.5040409@aei.mpg.de> <516DD433.50100@tigertech.com> <516DEAD4.7080305@bucksch.org> <516DFC4F.5000908@websitemanagers.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <516DFC4F.5000908@websitemanagers.com.au> Sender: linux-raid-owner@vger.kernel.org To: Adam Goryachev Cc: Robert L Mathews , Linux RAID List-Id: linux-raid.ids Adam Goryachev wrote, On 17.04.2013 03:35: > Obviously, if they suffered a two disk failure then they won't be here > asking for help will they:) Wrong, sadly. I suffered a 1 disk failure, and I am here asking for help. And nobody can give it. Again: I have a RAID5, and 1 (one) disk failed, so I should be fine, but I cannot read the data anymore, no way to get at it. That's because md ejected a good (!) drive to start with, and refuses to take it back (!). (And then another drive failed during resync.) If you have a way, please do show me, see thread 'Disk wrongly marked "spare", need to force re-add it' The problem isn't double disk failure. The problem is bugs in md implementation. > The Linux kernel advises Linux md that the block > device is gone, so Linux md discards the block device and stops trying > to use it. Personally, I don't see that Linux md has a lot of choice in > the matter True. But often, such errors are temporary. For example, a loose cable. I must be able to re-add the device as a good device with data. But I can't, md doesn't let me. My case was even more unbelievable: md ejected perfectly good drives simply because I upgraded the OS. (This happened with 2 independent arrays, so not coincidence.) Also, a single sector being unreadable/unwritable doesn't count as "disk failure" in my book, and shouldn't eject the whole disk. If I have 2 sectors on 2 different disks that are unreadable, md currently trashes the whole array and doesn't let me read anything at all anymore. That's obviously broken, but unfortunately the sad reality. See http://neil.brown.name/blog/20110216044002#1 (And, BTW, RAID6 doesn't really help with this problem, because it's quite possible that 3 disks have sectors unreadable/unwritable.)