I have in a test environment, 6 files VHDX "parent disks" hosted on a 60 gb SSD hard drive used for Hyper-V role. This saves about 68% of total storage space. I think it's one of the conditions recommended because files VHDX "parent disks" are read-only and the SSD drive has no other reason to be written by other processes. Thus, the deduplication process is fully optimized.