I have a storage pool on my Windows 11 system that is configured like this. 
I want to remove one of the physical disks from this pool.
From the UI, it seems I can only Extend the pool size.
From Powershell, I tried resize-virtualdisk -FriendlyName "TieredDisk" -Size (607GB), but got this error:
resize-virtualdisk : Not Supported Extended information: The Windows Storage Provider does not support shrinking virtual disks. I wonder if I forgot to install some system tools. If MS does not support resizing a virtual disk, why do they provide this command?