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 22:05:24 +0100 Message-ID: <563D1614.5010501@redhat.com> References: <1446688954-29589-1-git-send-email-samitolvanen@google.com> <563B066C.6050202@redhat.com> <20151106190634.GA2813@google.com> <563CFD6F.4040009@redhat.com> <20151106202750.GA11849@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20151106202750.GA11849@google.com> Sender: linux-kernel-owner@vger.kernel.org To: device-mapper development Cc: Will Drewry , Kees Cook , Mike Snitzer , Mandeep Baines , linux-kernel@vger.kernel.org, Mikulas Patocka , Mark Salyzyn List-Id: dm-devel.ids Dne 6.11.2015 v 21:27 Sami Tolvanen napsal(a): > On Fri, Nov 06, 2015 at 08:20:15PM +0100, Zdenek Kabelac wrote: >> i.e. you have 1G of space - you want to give 250MB as 'redundancy' - >> so create 4 partition.... well data safety has it's price - user should choose what he prefers - more games and videos or more safety... > > We cannot afford to set aside 25% of read-only partition space for > redundancy on mobile devices, and would rather not impact performance > any more than dm-verity already does. With error correction we have > 0.8% space overhead in our use case and no performance degradation if > the partition is not corrupted. > I'm probably missing here some hw knowledge here - but if you loose a flash block of some size - then you typically get 'error' for all bytes the sector/block. So how do you want to correctly 'restore' missing full sectors with just 0.8% data overhead ?? Or is the device which fails to correct block returning something 'still usable' (since e.g. SATA disk certainly not) Zdenek