On Fri, Aug 10, 2012 at 10:14 PM, Stefan Priebe - Profihost AG
<s.pri...@profihost.ag> wrote:
> Am 10.08.2012 14:04, schrieb ronnie sahlberg:
>
>> On Fri, Aug 10, 2012 at 9:57 PM, Stefan Priebe - Profihost AG
>> <s.pri...@profihost.ag> wrote:
>>>
>>> Am 10.08.2012 13:12, schrieb ronnie sahlberg:
>>>
>>>> You want discard to work?
>>>
>>>
>>> Yes
>>>
>>>
>>>> You are using qemu 1.0 ?
>>>
>>>
>>> actual qemu-kvm git
>>>
>>>
>>>> So you dont have the qemu support for scsi-generic passthrough to iscsi
>>>> devices.
>>>
>>>
>>> Why?
>>>
>>
>> scsi-generic passthrough I think was added for iscsi in 1.1
>> so in 1.0 your guest will talk scsi to qemu, and invoke the
>> scsi-emulation in qemu.
>> It then will call functions like 'bdrv_aio_discard()" in libiscsi
>> that will translate it back into a scsi command again and pass it to
>> the target.
>>
>> It still works, it just means you have a small degradation of
>> performance compared to if you could send the SCSI CDB straight
>> through to the iscsi target as you can in qemu 1.1
>> Very likely so small performance hit that you can not even measure it.
>
>
> which version are you talking about? I use qemu-kvm.git so this is upcomming
> 1.2 and i use libiscsi 1.5.0.
I dont know the kvm version numbers.
But you can check the file
block/iscsi.c for the version you use for this :
.bdrv_aio_discard = iscsi_aio_discard,
If it has bdrv_aio_discard then you have support for 'discard' when
using the scsi emulation. i.e. -drive ...,if=scsi,...
#ifdef __linux__
.bdrv_ioctl = iscsi_ioctl,
.bdrv_aio_ioctl = iscsi_aio_ioctl,
#endif
If it has these two lines too, then you have scsi-passthrough and can
bypass the qemu scsi emulation.
One way to activate passthough is via scsi-generic:
Example:
-device lsi -device scsi-generic,drive=MyISCSI \
-drive file=iscsi://10.1.1.125/iqn.ronnie.test/1,if=none,id=MyI
regards
ronnie sahlberg
