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

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Message-ID: <20151106212338.GA19557@google.com>
Date:	Fri, 6 Nov 2015 21:23:38 +0000
From:	Sami Tolvanen <samitolvanen@...gle.com>
To:	device-mapper development <dm-devel@...hat.com>
Cc:	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,
	Mikulas Patocka <mpatocka@...hat.com>,
	Mark Salyzyn <salyzyn@...gle.com>
Subject: Re: [dm-devel] [PATCH 0/4] dm verity: add support for error
 correction

On Fri, Nov 06, 2015 at 10:05:24PM +0100, Zdenek Kabelac wrote:
> So how do you want to correctly 'restore'  missing full sectors
> with just 0.8% data overhead ??

We use interleaving. Each byte in a 4k block is part of a different
Reed-Solomon block, which means an entire lost 4k data block looks like a
single error. When we also spread the bytes that form a single Reed-Solomon
block across the partition, we end up being able to correct several
megabytes of consecutive corrupted blocks with very small space overhead.

Sami
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