Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757565AbbKFTUV (ORCPT ); Fri, 6 Nov 2015 14:20:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36504 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751284AbbKFTUT (ORCPT ); Fri, 6 Nov 2015 14:20:19 -0500 Subject: Re: [dm-devel] [PATCH 0/4] dm verity: add support for error correction To: device-mapper development , Mikulas Patocka References: <1446688954-29589-1-git-send-email-samitolvanen@google.com> <563B066C.6050202@redhat.com> <20151106190634.GA2813@google.com> Cc: Will Drewry , Kees Cook , Mike Snitzer , Mandeep Baines , linux-kernel@vger.kernel.org, Mark Salyzyn From: Zdenek Kabelac Organization: Red Hat Message-ID: <563CFD6F.4040009@redhat.com> Date: Fri, 6 Nov 2015 20:20:15 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20151106190634.GA2813@google.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2375 Lines: 57 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/