On Fri, Aug 10, 2012 at 9:57 PM, Stefan Priebe - Profihost AG
<address@hidden> 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.