linux-kernel - Re: Linux kernel - Libata bad block error handling to user mode program

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Message-ID: <4B8FC6AC.4060801@teksavvy.com>
Date:	Thu, 04 Mar 2010 09:41:48 -0500
From:	Mark Lord <kernel@...savvy.com>
To:	Greg Freemyer <greg.freemyer@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	foo saa <foosaa@...il.com>, linux-kernel@...r.kernel.org,
	linux-ide@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>,
	linux-mm@...ck.org
Subject: Re: Linux kernel - Libata bad block error handling to user mode 
 program

On 03/04/10 09:17, Greg Freemyer wrote:
..
> I think / suspect your major problem is you say above that you use a
> 512-byte buffer to wipe with.  The kernel is using 4K pages.  So when
> you write to a 4K section of the drive for the first time, the kernel
> implements read-modify-write logic.
>
> Your i/o failures are almost certainly on the read cycle of the above,
> not the write cycle.  You need to move to 4K buffers and you need to
> ensure your 4K writes are aligned with how the kernel is working with
> the disk.  ie. You need your 4K buffer to perfectly align with the
> kernels 4K block handling so you never have a read-modify-write cycle.
..

You'll also need to disable Linux read-ahead for the drive,
or it may try reading beyond even the 4KB block.

But really.. isn't "hdparm --security-erase NULL /dev/sdX" good enough ???

Cheers
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