linux-kernel - Re: SATA hdd refuses to reallocate a sector?

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Message-Id: <201306260811.15421.linux@rainbow-software.org>
Date:	Wed, 26 Jun 2013 08:11:15 +0200
From:	Ondrej Zary <linux@...nbow-software.org>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	Mark Lord <mlord@...ox.com>, Pavel Machek <pavel@....cz>,
	Marcus Overhagen <marcus.overhagen@...il.com>,
	kernel list <linux-kernel@...r.kernel.org>,
	linux-ide@...r.kernel.org, tj@...nel.org
Subject: Re: SATA hdd refuses to reallocate a sector?

On Wednesday 26 June 2013, James Bottomley wrote:
> On Mon, 2013-06-24 at 08:18 -0400, Mark Lord wrote:
> > And the SCSI stack in Linux has rather atrocious error handling.
> > It lumps multiple requests together, and can fail the entire lot even
> > if only a single sector is bad.
>
> That's rather misleading.  SCSI doesn't lump anything together; it
> handles the requests it was passed.  For reads and writes through the
> page cache, block will aggregate in the elevators, but you avoid that by
> not using the page cache (O_DIRECT or SG_IO).

Yes, it works fine with O_DIRECT - that's why hdd_realloc reads 
sector-by-sector when an error was detected. I'd also like to disable read 
retries but that does not seem to be possible.

> For devices which report failing sectors correctly data up to the failed
> sector is returned and the request is shortened and retried from the
> failed sector on.  If we get a second failure at the beginning (where
> the previous bad sector was), then we give up.
>
> James


-- 
Ondrej Zary
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