I think you will get the best performance using direct LUN.
Is direct LUN using the QEMU iSCSI initiator, or SG_IO, and if so is it using /dev/sg or has that been fixed? SG_IO is definitely not going to be the fastest, especially with /dev/sg.
Storage
domain is best if you want
to use features provided by storage domain. If your important feature
is performance, you want
to connect the storage in the most direct way to your VM.
Agreed but you want a virtio-blk device, not SG_IO; direct LUN with SG_IO is only recommended if you want to do clustering and other stuff that requires SCSI-level access.
Paolo
Mordechai, did we do any similar performance tests in our lab?
Do you have example results?
Nir