Problems

Rent collector is seek-intensive
i.e. SLOW
No way to locate process objects
Resuming processes involve reading *all* header blocks
No concept of locality
no optimisations for inter-object relationships
Low Parallelism
Caching of remote objects difficult
Resizing the volume is tricky at best

Ignores totally
When resuming a process object, all objects mapped by it must be consistent with what the process last saw.