Re: [Qemu-devel] virtio-scsi vs. virtio-blk

[Stefan Priebe - Profihost AG <s.priebe@profihost.ag>]

http://www.nexenta.com/corp/products/what-is-openstorage/nexentastor

tells me:
"SCSI UNMAP as a client-side feature frees up storage in the back end, 
in the context of thin provisioning (a 100-to-one reduction in space for 
VDI when using NexentaStor)."

So i would say nexenta supports it. But i'm using virtio-scsi-pci? I'm 
really sorry to ask so many questions.

Stefan
Am 10.08.2012 13:20, schrieb ronnie sahlberg:
> On Fri, Aug 10, 2012 at 8:30 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Il 10/08/2012 12:28, Stefan Priebe - Profihost AG ha scritto:
>>> I'm using iscsi. So no raw or qcow2.
>>
>> Ok, then you need to use scsi-block as your device instead of scsi-disk
>> or scsi-hd.  This will disable the QEMU SCSI emulation and let your VM
>> talk directly to the NAS.
>>
>> CCing Ronnie who may be interested in bug reports since I'm on holiday
>> starting "soon".
>>
>
> I think it works on any,
> You can of course not boot from a if=scsi disk in qemu,
>
> but any '-drive file=iscsi://...,if=scsi' should work as long as it is
> not the boot device.
>
> SCSI emulation in qemu picks this up via WRITESAME10/16 and then calls
>   bdrv_aio_discard()
> block/iscsi.c is invoked for discard and then translates this back to
> a SBC UNMAP command it sends to the target.
>
>
> Now, block/iscsi.c does assume that any target that reports that it
> supports thin-provisioning actually implements UNMAP command.
> There could be targets that support thin-provision ing that does NOT
> support UNMAP and unly support discard via WRITESAME10/16
> so at some stage I should send a patch to iscsi.c to check which
> commands the target supprots and use one of the supported ones instead
> of a blanket
> "you say you support thin-provisioning, I take that as confirmation
> you support SBC UNMAP"
>
>
> regards
> ronnie sahlberg
>