linux-kernel - Re: [dm-devel] [PATCH 0/4] dm verity: add support for error correction

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Message-ID: <alpine.LRH.2.02.1511071018250.18330@file01.intranet.prod.int.rdu2.redhat.com>
Date:	Sat, 7 Nov 2015 10:20:38 -0500 (EST)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Sami Tolvanen <samitolvanen@...gle.com>
cc:	device-mapper development <dm-devel@...hat.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>,
	Mike Snitzer <snitzer@...hat.com>,
	Mandeep Baines <msb@...omium.org>,
	linux-kernel@...r.kernel.org, Mark Salyzyn <salyzyn@...gle.com>
Subject: Re: [dm-devel] [PATCH 0/4] dm verity: add support for error
 correction



On Fri, 6 Nov 2015, Sami Tolvanen wrote:

> 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....
> 
> We cannot afford to set aside 25% of read-only partition space for

You can have 20 raid5 legs (with as big chunksizes as possible - so that 
sequential accesses are really sequential when they hit the flash device), 
and that means setting aside only 5%. Or even more legs.

Mikulas

> 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.
> 
> Sami
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