From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jon Nelson Subject: Re: RAID6 dead on the water after Controller failure Date: Sat, 15 Feb 2014 17:23:28 -0600 Message-ID: References: <7A417EAE-106E-4541-941F-1002696F8735@gmail.com> <52FE7E2D.8020308@turmel.org> <5269CCC7-A0A7-479E-9738-88C74CB19435@gmail.com> <52FF83F1.3030904@turmel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Mikael Abrahamsson Cc: Phil Turmel , Florian Lampel , LinuxRaid List-Id: linux-raid.ids On Sat, Feb 15, 2014 at 5:04 PM, Mikael Abrahamsson wrote: > On Sat, 15 Feb 2014, Jon Nelson wrote: > >> Out of 12 drives, I thought RAID6 only offered a total of *2* failed >> devices. It seems to me that you have 7 devices in sync and 4 *almost* in >> sync. It's this "almost" part that has me confused. How can the raid run if >> the event count doesn't match? Wouldn't at least 10 out of 12 drives have to >> have the same event count to avoid data loss? > > > Correct. When you use --assemble --force you're basically telling mdadm "I > know what I'm doing and I'll take the risk of data loss or corruption". If > you assemble in with a kicked drive that was kicked long ago that has a > really far off event count, you can really really screw things up. > > Unless you use --force, mdadm won't assemble an array where the event count > doesn't match up. Aha. So if you ran a check in this case, it would find some number of blocks that don't match up. What does MD do in that case? -- Jon