We have a Windows 2012 Veeam Server with a volume that we use to store our backups on. The volume has a capacity of 14.9 TB and has data deduplication enabled.

On the volume there are folders for the different backup jobs. These folders have a smaller size on disk than their actual size due to data deduplication. The sum of the size on disk of all the folders is about 8 TB, but windows shows that there's only 64 KB free space left on the disk.

The folder option to show hidden files, folders and drives is enabled.

Does anyone know how I can see why there's a discrepancy between the sum of the size on disk of the folders and the free space left on the disk?

  • Been a while since I've worked with Windows, but could it be volume shadow copies? – Alex Forbes Feb 5 '18 at 15:16
  • Shadow copies are disabled on the drive. – Skanderbeg Feb 5 '18 at 16:17
  • Have you ran a diskspace scan like Treesize? – pxed Feb 5 '18 at 18:53

With deduplication turned on, the "size on disk" value is meaningless. It'll just tell you the amount of disk space used by the not (or not yet) deduplicated or compressed files fragments.

E.g. if you've got two 10 GB files that share 8 GB identical data and differ only in 2 GB, both files will show only 2 GB "size on disk" while 8 GB deduplicated data is hidden. If those 2 GB are even compressible, the file shows 0 "size on disk".

Deduplicated data is hidden in System Volume Information and is normally invisible. Even if you make it visible you can't make out which parts go where.

If you delete files to free up space you need to additionally run garbage collection to free up the unused, deduplicated chunks as well (dedupcli enqueue /gc /vol X:).

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