linux-kernel - Re: [PATCH 2/2] Drivers: scsi: storvsc: Force discovery of LUNs that may have been removed.

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Date:	Fri, 29 Aug 2014 08:19:11 +0200
From:	Hannes Reinecke <hare@...e.de>
To:	Mike Christie <michaelc@...wisc.edu>,
	Christoph Hellwig <hch@...radead.org>,
	"K. Y. Srinivasan" <kys@...rosoft.com>
CC:	linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
	ohering@...e.com, jbottomley@...allels.com,
	linux-scsi@...r.kernel.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH 2/2] Drivers: scsi: storvsc: Force discovery of LUNs that
 may have been removed.

On 08/29/2014 04:42 AM, Mike Christie wrote:
> On 08/27/2014 09:31 AM, Hannes Reinecke wrote:
>> On 08/19/2014 07:54 PM, Christoph Hellwig wrote:
>>> On Sat, Aug 16, 2014 at 08:09:48PM -0700, K. Y. Srinivasan wrote:
>>>> The host asks the guest to scan when a LUN is removed or added.
>>>> The only way a guest can identify the removed LUN is when an I/O is
>>>> attempted on a removed LUN - the SRB status code indicates that the LUN
>>>> is invalid. We currently handle this SRB status and remove the device.
>>>>
>>>> Rather than waiting for an I/O to remove the device, force the
>>>> discovery of
>>>> LUNs that may have been removed prior to discovering LUNs that may have
>>>> been added.
>>>
>>> This looks pretty reasonable to me, but I wonder if we should move this
>>> up to common code so that it happens for any host rescan triggered by
>>> sysfs or other drivers as well.
>>>
>> Not without proper testing.
>> Currently we cannot rescan existing devices; the inquiry string is
>> nailed to the sdev structure. The only way to really refresh the
>> information is to delete it and rescan it again.
>
> How are distros handling 0x6/0x3f/0x0e (report luns changed) when it
> gets passed to userspace? Is everyone kicking off a new full (add and
> delete) scan to handle this or logging it? Is the driver returning this
> when the LUNs change?
>
Currently it's logged to userspace and ignored.
Doing an automated rescan has proven to be dangerous, as it
might disconnect any LUNs which are still in use by applications.
Especially HA or database setups tends to become very annoyed
when you do an automated rescan.

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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