I deleted several hyper-v snapshots to free up some space on my deduplicated nvme drive on my Lenovo P1 hyper-v lab, as it was starting to get low. Below is roughly how much space was on the de-duplicated drive after deleting the snapshots but before running the PowerShell script.
After hyper-v was finished with it’s disk activities (use Resource Monitor to confirm when that is finished) from deleting snapshots I ran the following PowerShell.
Start-DedupJob D: -Type GarbageCollection -full get-dedupjob
After running the script you can use get-dedupjob over and over to see the status.