But for storing the redundant information, additional space is needed. These disks will appear as one logical volume and the failure of a single disk will not cause any data loss. Another possibility is that you are using a Software RAID - like Windows offers - which spreads the data with redundancy over several disks.

This is usually 0.5 - 2% of the occupied space. It is not possible to free this space with TreeSize Free or any other tool. Beyond the space that is needed for storing the files itself, additional space is used for storing management data like the File Allocation Table of the file system or the boot sector. Turn on 'View > Options > Show Errors Messages' to be notified if a folder cannot be scanned. Therefore it is highly recommended to run TreeSize Free as administrator. Another reason for this difference can be that not all parts of the drive could be scanned due to access restrictions.

Please make sure that you have the view option 'Allocated Space' activated when you are interested in the physically allocated space.

The Windows Explorer shows the space that is physically allocated on the drive while TreeSize Free shows the space that is occupied by all files under a certain path.

The allocated space that Windows shows in the properties dialog of the drive may be larger than the allocated space reported by TreeSize Free.

Provided are instructions and information which makes understanding of TreeSize and how to use it easier.

Treesize free from jam software