NTFS Deduplication Sizes

Question / Problem

If the NTFS deduplication (available for Windows Server 2012 and higher) is enabled, TreeSize displays some strange values for the size of files and folders. A lot of files have a size of "0 Byte" while a folder called "System Volume Information" requires a huge amount of disk space. What is the reason for this?

Answer / Solution

The NTFS deduplication segments files with fractionally equal content into so-called "chunks" which are moved into a the subfolder "System Volume Informaton\Dedup\ChunkStore\" (SVI) located on the corresponding NTFS partition. After the deduplication has been applied, the original files are replaced by a pointer to the corresponding chunk in the SVI directory. Two identical files will only require half of the disk space they occupied before after a NTFS deduplication. Since the original files now only contain a small pointer, the allocated disk space will be indicated by Windows with a much smaller value than before (for two identical files the occupied disk space would be indicated as "0 Byte"). To make TreeSize show the original file and folder sizes again, simply switch the view mode from "Allocated Space" to "Size". The allocated size shown in TreeSize is the disk space you would obtain by deleting the corresponding file