From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wols Lists Subject: Re: Rewrite md raid1 member Date: Fri, 19 Aug 2016 12:52:21 +0100 Message-ID: <57B6F2F5.8090800@youngman.org.uk> References: <20160818030451.GA17225@onthe.net.au> <2dca8e1f-8e80-408f-900e-36f9b1dd6f95@fnarfbargle.com> <20160818040151.GA21256@onthe.net.au> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160818040151.GA21256@onthe.net.au> Sender: linux-raid-owner@vger.kernel.org To: Chris Dunlop , Brad Campbell Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 18/08/16 05:01, Chris Dunlop wrote: > I'm interested to see if there's a way of essentially doing the above on a > live system, assuming there's appropriate care taken to not trash any > existing data (including superblocks). > > I.e. is it *theoretically* possible to write the same data back to the whole > disk safely. E.g. using 'dd' from/to the same disk is almost there, but, as > described, there's a window of opportunity where you could get stale data on > the disk and a raid repair could then copy that stale data to the good disk. There is something called "scrub". My superficial knowledge of raid doesn't let me know what it is, but as far as I can make out it forces a whole-disk-write or somesuch. Explicitly to flush out such problems. If someone else can tell you how to scrub your disks, I'd try that. It's especially recommended, I think, for people with desktop drives in their array because it flushes out pending problems, which with desktop drives typically remove the "R" from "raid". Cheers, Wol