From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dark Penguin Subject: Re: Why not just return an error? Date: Fri, 7 Oct 2016 20:44:37 +0300 Message-ID: <57F7DF05.8090605@yandex.ru> References: <57F6DF18.40703@yandex.ru> <20161007112151.GA4405@metamorpher.de> <57F7CC10.3050607@yandex.ru> <94b1a4f4-adec-90b7-e804-2d8d2c94a7af@turmel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <94b1a4f4-adec-90b7-e804-2d8d2c94a7af@turmel.org> Sender: linux-raid-owner@vger.kernel.org To: Phil Turmel , Andreas Klauer , Rudy Zijlstra , keld@keldix.com Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 07/10/16 19:52, Phil Turmel wrote: > Hi DP, > > {It's good that you are trimming replies, but don't cut the ID of who > wrote what. } Oh, yeah, sorry. > You want to push the failure condition from being "broken raid with > likely salvageable data, except for one sector" to "repeated errors to > the upper layers with unknowable corruption as side effects". That actually describes it pretty well, yes. %) Being able to choose a failure condition most suitable for your specific situation, and being able to push it that far and still have a working RAID if you want that. > Then patch your kernel with your desired behavior. "Free software" > doesn't mean someone writes what you want for free. And I disagree with > you, so would object to it being put in the mainline kernel. Yes, that's one of the things on my TODO list once I become a developer able to do that. :) I just thought I'm probably not the only one who wants that, and so I wanted to learn why is it not possible. And listen to what other people really think about it. >> Anyway, if I had a collapsed RAID-5, I would want to at least have an >> easy option to start it in a read-only mode in the last-known working >> state, while the faulty drives are still not out of sync, and recover >> data easily (to my single backup drive), or continue using the array for >> a while, manually deleting one "bad" file if necessary; this is of >> course not a "good thing" to do, but this way, RAID would be at least >> not worse than single drives with faulty sectors, which are capable of >> that, while RAIDs are not! I would be fine with that in my archive - as >> I'm fine with some less importand parts of the archive being on faulty >> single drives. It's just that I don't want to lose the whole drive due >> to a hardware failure - and RAID adds more causes other than that, >> instead of offering more protection against that. > > MD raid has no idea what is at any given sector. And with a > near-infinite variety of layering choices, there's no way it's going to. > That's why *you* have to do this. You trimmed my description of the > only "easy option" actually trustable. I actually wanted to ask about that. Can you really ddrescue a drive with a "hole" in it, re-add it and expect it to work?.. What happens if you try to read from that "hole" again? And while I'm talking about re-adding, when does it become impossible to "re-add" a drive?.. -- darkpenguin