From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zdenek Kabelac Subject: Re: [dm-devel] [PATCH 0/4] dm verity: add support for error correction Date: Fri, 6 Nov 2015 20:20:15 +0100 Message-ID: <563CFD6F.4040009@redhat.com> References: <1446688954-29589-1-git-send-email-samitolvanen@google.com> <563B066C.6050202@redhat.com> <20151106190634.GA2813@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20151106190634.GA2813@google.com> Sender: linux-kernel-owner@vger.kernel.org To: device-mapper development , Mikulas Patocka Cc: Will Drewry , Kees Cook , Mike Snitzer , Mandeep Baines , linux-kernel@vger.kernel.org, Mark Salyzyn List-Id: dm-devel.ids Dne 6.11.2015 v 20:06 Sami Tolvanen napsal(a): > On Fri, Nov 06, 2015 at 12:23:29PM -0500, Mikulas Patocka wrote: >> I'm also wondering what is this patch useful for. Disks and flash >> controllers have their own error detection and correction > > I think I addressed this earlier. Some storage devices are able to > correct bit flips, but don't have enough redundancy to correct larger > errors. Using this patch set we can correct N MiB of consecutive > corruption anywhere on the partition with the same amount of storage > overhead. > >> Another point - if the read-only system partition is experiencing some >> errors, than the read-write partition will probably have errors too > > On mobile devices, errors in read-only partitions often lead to > bricked devices while errors in the read-write parts might only lead > to lost cat photos. There are situations where people would prefer to > have a working phone even if it fails to store some of their data. > >> Do you have some real case where such error corrections >> increase longevity of some device? > > Yes, there have been several cases where read-only partition errors > have rendered a device unusable. The sheer volume of mobile devices > means that even if a tiny fraction of them suffer from such a problem, > it's going to affect a large number of people. > >> But you can take raid5 in read-only mode, put it on several partitions >> protected with dm-verity and you get decent error correction > > I agree. Unfortunately, we don't currently have the luxury of using > raid on mobile devices. AFAIK - you just build as much partition as need to have some 'space' dedicated for redundancy - and rest of 'partitions' you join as 'writable' i.e. you have 1G of space - you want to give 250MB as 'redundancy' - so create 4 partition.... Since phones starts to have 64GB of storage space - it looks like a way to go..... As no one bothers to upgrade 'old' phone - why to focus there?? And BTW - already seen couple bricked Nexus7.... (And no marhmallow in plan....) (And interestingly all killed I've seen were on Lolipop - none with Kitkat) Zdenek