MSDP shows a significant amount of used space, when there are zero images in the NetBackup catalog on that storage unit.
NetBackup space reclamation processing does not reclaim the space.
The OS reports that the size for that MSDP volume is significantly lower than the amount MSDP claims is used, and the "Size on Disk" is even lower. This is an indicator that Windows Deduplication is being used, even if the volume format is being reported as NTFS basic, simple.
none, just not releasing the space.
Windows Deduplication has been turned on as some point while this drive was used as MSDP. (It is NOT recommended to run MSDP storage on a Windows 2012 NTFS deduplicated volumes.) It had since been turned back off, but it had not been cleaned up first.
1. Re-enable Windows Deduplication for the volume housing the MSDP storage.
2. Run the utilities provided by Windows ('garbage collection' and 'garbage scrubbing').
3. After a few hours, the space should return to normal.
4. Turn the Windows Deduplication feature off at that point, when the drive is clean.
Windows 2012 and higher (as an MSDP media server); NetBackup 7.6 and higher.
(Windows 2012 R2 requires 220.127.116.11 or higher to run as a media server.)