How to reclaim space from deleted files on windows server deduplication volume

Windows server has great deduplication functionality allowing for increased usable capacity on non-operating system volumes, by performing block level deduplication to increase storage efficiency. This is particularly useful for storing data such as backups, which often involves minimal changing data, so a prime candidate for effective deduplication.

The problem often encountered with deduplication volumes is that when files are deleted, the space is not immediately reclaimed by the operating system. A "garbage collection" process needs to be run in order for the deduplication engine to reclaim this space.

Thankfully, this is incredibly easy to do and can be done from a powershell command prompt - here's the command you need to run;

start-dedupjob -type GarbageCollection -full -path e: -FastStart $true

Be sure to change the -path variable from E: to whatever drive you wish to run the garbage collection on. Also note that depending on the size of your volume, the garbage collection can take some time to initiate and complete, even with using the -FastStart switch.

You can check the progress of your deduplication jobs by running the command

get-dedupjob