linux-kernel - Re: [Patch] SCSI: Retrieve Cache Mode Using SG_ATA

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Date:	Tue, 11 Oct 2011 12:41:34 +0200
From:	Hannes Reinecke <hare@...e.de>
To:	Amit Sahrawat <amit.sahrawat83@...il.com>
Cc:	James Bottomley <James.Bottomley@...senpartnership.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Douglas Gilbert <dgilbert@...erlog.com>,
	linux-usb@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	NamJae Jeon <linkinjeon@...il.com>
Subject: Re: [Patch] SCSI: Retrieve Cache Mode Using SG_ATA_16 if normal routine
 fails

On 10/11/2011 10:26 AM, Amit Sahrawat wrote:
> SCSI: Retrieve Cache Mode Using SG_ATA_16 if normal routine fails
>
> It has been observed that a number of USB HDD's do not respond correctly
> to SCSI mode sense command(retrieve caching pages) which results in their
> Write Cache being discarded by queue requests i.e., WCE if left set to
> '0'(disabled). So, in order to identify the devices correctly - give it
> a last try using SG_ATA_16 after failure from normal routine.
>
I'd be _VERY_ cautious when trying something like this.

ATA_16 is a rather recent command, and most older drives simply 
can't cope with this. Instead they just kick the error handler and 
go offline eventually.

Shouldn't we rather use a sensible default, ie assume WCE is enabled?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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