From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wols Lists Subject: Re: 4.11.2: reshape raid5 -> raid6 atop bcache deadlocks at start on md_attr_store / raid5_make_request Date: Mon, 22 May 2017 20:07:18 +0100 Message-ID: <592336E6.8080906@youngman.org.uk> References: <87lgppz221.fsf@esperi.org.uk> <87a865jf9a.fsf@notabene.neil.brown.name> <87o9ukykmk.fsf@esperi.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <87o9ukykmk.fsf@esperi.org.uk> Sender: linux-raid-owner@vger.kernel.org To: Nix , NeilBrown Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 22/05/17 16:30, Nix wrote: > I'll give it a try -- I hit it twice in succession, once with a > --backup-file, once without. Since mdadm does not warn about the lack of > a --backup-file, I guess the statement in the manual that it is > essential to provide one when changing RAID levels is untrue: I suspect > that it's necessary *if* you're not increasing the number of disks at > the same time, but since I'm growing into a spare, adding a > --backup-file only slows it down? I did discuss this with Neil while I wrote it, so I hope I got it right :-) https://raid.wiki.kernel.org/index.php/A_guide_to_mdadm#Array_internals_and_how_it_affects_mdadm aiui, provided you're using a v1 superblock, the data offset means there is spare space on the drives precisely for the purpose (one of then at least) of keeping a backup. So the reshape will start reshaping into the spare space and eliminate the need for the backup - the new version of the stripe will be safely written before the space occupied by the old stripe is required. Cheers, Wol