I have a storage pool made up from 7 physical desktop drives all attached to the motherboard SATA ports.
Seagate 4TB (x4)
Western Digital 2TB (x1)
Western Digital 500GB (x2)
Pool size: 17.3TB (as repored by Win)
The problem seems to be with Thin disks, they use up free pool space when i copy files to the virtual disk but when i delete the files only part of the allocated space is returned. To test this out more thoroughly i created a new "2-Way Mirror Thin ReFS" disk and copied about 650GB to it, waited until next day, and promptly deleted it all. The virtual disk was now empty, yet it still allocated about 680GB from the pool which would not be returned until the virtual disk itself was deleted.
My largest virtual storage disk (2-Way Mirror Thin ReFS) now has 2TB+ "Ghost" allocation that it refuses to return to the pool and it keeps growing whenever i make any changes. The data on this virtual disk exceeds my other free disk space elsewhere so i cant move all the data off it and recreate it. I need to fix it on the fly somehow and preferably without buying a ton of new diskspace.
I tried Optimize-Volume as suggested on a bunch of google search results with the following result:
PS C:\Users\Administrator> Optimize-Volume -DriveLetter E -Verbose -ReTrim -SlabConsolidateVERBOSE: Invoking slab consolidation on Storage1 (E:)...
VERBOSE: Slab Analysis: 0% complete...
Optimize-Volume : The specified extrinsic Method does not exist.
At line:1 char:1
+ Optimize-Volume -DriveLetter E -Verbose -ReTrim -SlabConsolidate
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : MetadataError: (MSFT_Volume (Ob...3-80ba-bcee...):ROOT/Microsoft/...age/MSFT_Volume) [Op
timize-Volume], CimException
+ FullyQualifiedErrorId : MI RESULT 17,Optimize-Volume