Should I use passthrough disks or iSCSI attached to the guest for storage?
The decision depends on what features you need to expose to the guest. In the passthrough case the drive will show up without knowledge of the underlying LUN. Educated guess: If you are looking for raw performance passthough will give you the best result. Reason: When doing IO from the guest using passthough you traverse the guest storage stack + disk stack in the root.
