From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wol's lists Subject: Re: force remapping a pending sector in sw raid5 array Date: Fri, 9 Feb 2018 22:07:57 +0000 Message-ID: <3345d6f0-80d0-bfaf-9974-a7472d499117@youngman.org.uk> References: <20180209192928.vliiwkv6q76jf6jp@merlins.org> <1227ce39-31af-22f2-f4fa-de85466f05c7@turmel.org> <20180209202958.6mieeomu5of45rjf@merlins.org> <59144df0-35b7-942f-22c8-754afd0f89c4@uni-konstanz.de> <20180206181416.amo6geclrvc6ylrf@merlins.org> <20180209192928.vliiwkv6q76jf6jp@merlins.org> <1227ce39-31af-22f2-f4fa-de85466f05c7@turmel.org> <20180209202958.6mieeomu5of45rjf@merlins.org> <5947e803-b1e8-b530-4935-df126f867213@turmel.org> <20180209212252.GN9565@merlins.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180209212252.GN9565@merlins.org> Content-Language: en-US Sender: linux-raid-owner@vger.kernel.org To: Marc MERLIN , Phil Turmel , Kay Diederichs Cc: Andreas Klauer , Adam Goryachev , Roger Heflin , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 09/02/18 21:22, Marc MERLIN wrote: > Interesting. I figured once a sector went pending once, it would not actually be re-used and > be remapped on the next write. Seems like it didn't happen here. Because there's all sorts of reasons a sector can go pending. My favourite example is to compare it to DRAM. DRAM needs refreshing every couple of seconds, otherwise it loses its contents and cannot be read, but it's perfectly okay to rewrite and re-use it. Likewise, the magnetism in a drive can decay such that the data is unreadable, but there's nothing actually wrong with the drive. (If the data next door is repeatedly rewritten, the rewrite can "leak" and trash nearby data ...) The decay time for that should be years. The problem of course is when the problem has a decay time measured in minutes or hours. The rewrite succeeds, so the sector doesn't get remapped, but when you next read it it has died :-( Cheers, Wol