From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Robinson Subject: Re: bug: 4-disk md raid10 far2 can be assembled clean with only two disks, causing silent data corruption Date: Wed, 26 Sep 2012 09:59:42 +0100 Message-ID: <5062C3FE.7090906@yuiop.co.uk> References: <50606207.7040804@gooseman.cz> <20120925141959.0c22de7d@notabene.brown> <152edbf7bdad33717477f174f94116b7@192.168.93.35> <20120925223227.130ef8e3@notabene.brown> <50628B39.90205@gooseman.cz> <20120926154107.1568a115@notabene.brown> <20120926082848.GA18616@www5.open-std.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120926082848.GA18616@www5.open-std.org> Sender: linux-raid-owner@vger.kernel.org To: keld@keldix.com Cc: NeilBrown , Jakub Hus?k , Mikael Abrahamsson , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 26/09/2012 09:28, keld@keldix.com wrote: [...] > I also understand it now, I think. raid10,f2 with 4 disks cannot in the current implementation > survive 2 failing disks. It can, but only two non-adjacent discs. With 4 drives sda-sdd, than means you can only lose both sda and sdc, or sdb and sdd. > We have discussed earlier how to implement raid10,far that would mean > better survival chances with more disks failing. This is not implemented yet. No, but even if/when it is, there will still be some combinations of two discs that you cannot afford to lose. The layout change to try to improve redundancy will not be generic, as it doesn't work for an odd number of discs, so the existing layout would have to be retained as an option. Cheers, John. -- John Robinson, yuiop IT services 0131 557 9577 / 07771 784 058 46/12 Broughton Road, Edinburgh EH7 4EE