Win10 Storage Spaces - Mirrored Pool Doesn't Release Space

Using Storage Spaces for a simple Mirrored Pool with (2) 4TB HDD's for a backup drive.

Setup was simple and easy with Storage Spaces reporting a formatted 3.75TB Mirrored Volume.

After test writing some system images and doing some disk speeds tests, Storage Spaces says drives are over 80% full with a warning, but there isn't any kept data on there.

Under Computer Management, the Volume says only 15% used.

So it's like deleted files (also deleted from recycle bin) don't get reported as free space back to the Storage Space Console.

I have also created a SIMPLE storage space with (2) SSD's, but deleted files and space seems to be reclaimed there.

I have enabled Disk Optimizer to run once a week but it doesn't help to reclaim the space on the MIRRORED volume of HDD's.

Windows Version 2004 - 19041.572

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I think I may have gone down a rabbit hole and discovered what is going on.

Win Storage Spaces uses Thin Provisioning, which does not release the space to the OS, after file delete, it just deletes the index. You have to use a tool call SDelete from MSFT to truly zero out the space.

Thick vs Thin VMware Disk Provisioning: What is the Difference?