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

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

never used this tool. Output is:
This looks like this:
# sg_unmap --lba=0x1000 --num=1 /dev/sde

# sg_get_lba_status --lba=0x1000 /dev/sde
get LBA status: transport: Host_status=0x10 is invalid
Driver_status=0x08 [DRIVER_SENSE, SUGGEST_OK]

Get LBA Status command failed
     try '-v' option for more information

Stefan
Am 10.08.2012 13:58, schrieb ronnie sahlberg:
> You can easily verify if your target supports thin-provisioning via
> the UNMAP command.
>
> Download the sg3-utils package
>   and either mount the LUN locally via the kernel open-iscsi or apply
> the libiscsi patch to sg3-utils to make it iscsi-aware
>
> then use the commands    "sg_unmap"  to try to unmap regions   and
> "sg_get_lba_status" to check that the regions are now unmapped.
>
>
>
> On Fri, Aug 10, 2012 at 9:54 PM, Stefan Priebe - Profihost AG
> <s.priebe@profihost.ag> wrote:
>> 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
>>>
>>