Windows Explorer – How can an large file have a zero “Size on disk” value? What does it mean


I would expect some discrepancy between "Size" and "Size on disk" in Windows Explorer due to file system allocations etc.

Below is a screenshot of an example file on a Windows 2012 R2 file server that has a 81.4 MB "Size" but for the "Size on disk" it's 0 bytes. What gives?

I have other files doing the same, but yet another set of files and folders behaving as expected showing the size on disk relatively close to the actual file size.

The volume is a basic disk, formatted with NTFS and the default 4K allocation units.
No compression is set for any file or folder on the volume.
(For those more paranoid, I did a malware scan, and also confirmed there is not ADS streams associated with the file in question).

The user account running Windows Explorer is the domain administrator, and the file owner is also the domain administrator.

Thanks for reading!

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Best Answer

  • From the picture ou post I assume you use the new Feature Data Deduplication which stores multiple copies of a file only one time:

    Data deduplication involves finding and removing duplication within data without compromising its fidelity or integrity. The goal is to store more data in less space by segmenting files into small variable-sized chunks (32–128 KB), identifying duplicate chunks, and maintaining a single copy of each chunk. Redundant copies of the chunk are replaced by a reference to the single copy. The chunks are compressed and then organized into special container files in the System Volume Information folder.