linux-kernel - RFC: detection of silent corruption via ATA long sector reads

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Date:	Fri, 26 Dec 2008 16:44:57 -0500
From:	"Greg Freemyer" <greg.freemyer@...il.com>
To:	Redeeman <redeeman@...anurb.dk>
Cc:	piergiorgio.sartor@...go.de, neilb@...e.de,
	linux-raid@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	"Mark Lord" <liml@....ca>
Subject: RFC: detection of silent corruption via ATA long sector reads

All,

On the mdraid list, there was a recent thread about using raid
functionality to detect / repair silent corruption.

The issues brought up were that a lot of silent data corruption occurs
when cables, controllers, power supplies, ram, cache, etc. goes bad.

It made me think about another option for detecting silent corruption
I have not seen discussed, but maybe I missed it.

Aiui, the ATA spec allows for the reading of a long sector as well as
the normal 512 byte sector.  When you get a long sector you also get
the CRC (or whatever checksum data there is on the disk that allows
the drive itself to detect media errors).

I don't have any idea how easy or hard it would be to do, but I would
like to see the entire block subsystem enhanced to optionally allow
long sector reads to be used in a "paranoid" fashion.

Effectively it would be:

1) Read long sector from drive:  verify CRC in kernel.  This tests
most everything on the i/o path.

2) maintain CRC type information in block subsystem.  Verify no
corruption just before handing off to userspace.  This would
potentially identify CPU/cache/RAM failures.

Mark Lord has implemented long sector reads via hdparm.  Mark can you
comment on the feasibility of this idea?

Thanks
Greg
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