On 07/17/2012 11:11 AM, James Bottomley wrote:
> On Tue, 2012-07-17 at 10:54 +0200, Paolo Bonzini wrote:
>> Il 17/07/2012 10:40, James Bottomley ha scritto:
>>>>>
>>>>> It's not specific to virtio-scsi, in fact I expect that virtio-scsi will
>>>>> be almost always used with non-removable disks.
>>>>>
>>>>> However, QEMU's SCSI target is not used just for virtio-scsi (for
>>>>> example it can be used for USB storage), and it lets you mark a disk as
>>>>> removable---why? because there exists real hardware that presents itself
>>>>> as an SBC removable disk. The only thing that is specific to
>>>>> virtualization, is support for online resizing (which generates a unit
>>>>> attention condition CAPACITY DATA HAS CHANGED).
>>> So what's the problem? If you're doing pass through of a physical disk,
>>> we pick up removable from its inquiry string ... a physical removable
>>> device doesn't get resized. If you have a virtual disk you want to
>>> resize, you don't set the removable flag in the inquiry data.
>>
>> In practice people will do what you said, and it's not a problem.
>>
>> However, there's nothing that prevents you from running qemu with a
>> removable SCSI disk, and then resizing it. I would like this to work,
>> because SBC allows it and there's no reason why it shouldn't.
>
> There's no such thing in the market today as a removable disk that's
> resizeable. Removable disks are for things like backup cartridges and
> ageing jazz drives. Worse: most removeable devices today are USB card
> readers whose standards compliance varies from iffy to non existent.
> Resizeable disks are currently the province of storage arrays.
>
Ho-hum. I beg to disagree.
drivers/scsi/aacraid/aachba.c:2266
/* Do not cache partition table for arrays */
scsicmd->device->removable = 1;
To the extend of my knowledge aacraid does this _precisely_ to allow
for resizing; in effect every open() will trigger a device revalidation.
So I guess by just setting the 'removable' flag you should be okay.
You might need to remount it, but that's another story.
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
h...@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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