linux-kernel - Re: [PATCH 3/5] libata: Implement disk shock protection support

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Date:	Mon, 04 Aug 2008 23:12:04 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Elias Oltmanns <eo@...ensachen.de>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>, Jeff Garzik <jeff@...zik.org>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Pavel Machek <pavel@....cz>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] libata: Implement disk shock protection support

Elias Oltmanns wrote:
>> For libata, the easiest way to achieve the above would be adding a
>> per-dev EH action, say, ATA_EH_UNLOAD and schedule EH w/ the action OR'd
>> to eh_info->action.  The EH_UNLOAD handler can then issue the command
>> wait for the specified number of seconds and continue.  This will be
>> pretty simple to implement as command exclusion and stuff are all
>> automatically handled by EH framework.
> 
> I'm rather afraid this approach is impractical or unfavourable at the
> very least. Depending on the configured thresholds, a head unload
> request might well be issued unintentionally, e.g. by accidentally
> knocking against the table. It is quite alright for the HD to stop I/O
> for a moment but if the secondary device on the interface happens to be
> a CD writer, it will be very annoying to have CD writing operations fail
> due to minor percussions.

Why would it fail?

> Also, if there are two devices on the same
> port that support the UNLOAD FEATURE and you issue a head unload request
> to both of them in close succession, the IDLE IMMEDIATE to the second
> device will be blocked until the timeout for the first has expired.

Unload can be implemented as port-wide operation so that it issues IDLE
IMMEDIATE to all drives on the port but given that this is mostly for
laptop, this discussion is a bit peripheral.

-- 
tejun
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