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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!

enter image description here

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    I note in your screenshot that your path is reporting D:\DFSRoots Is that just a coincidental name or are you using DFS (Distributed File System)? With DFS the file may not necessary live locally on the server you are on but will reside wherever the DFS has been set up and the partner set up in the DFS relationship. As a result, the physical size on disk would be 0 bytes. – Enigman Aug 21 '14 at 10:37
  • @Enigman Keen eyes :-) Yes, we are using DFS but there is no replication partner and this screenshot is local to the server where this is setup. – Jaans Aug 21 '14 at 11:45
  • Update: I just did a little test and found that if I copy a file like the one above, then the newly copied file DOES have a "Size on disk" that is roughly equal to the size. I'm really confounded by this one. I have run chkdsk /r too, if it matters. – Jaans Aug 21 '14 at 11:48
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    Are you using the Deduplication feature? Maybe the file is stored somewhere else so this is only a link and uses no space. – magicandre1981 Aug 21 '14 at 16:08
  • @magicandre1981 By George... that's it! That explains it. Admittedly it was not very obvious to see that DeDup was being applied from the Windows Explorer, Disk Management or File Server Resource Manager tools. The following MSDN page confirms that the size on disk would be smaller technet.microsoft.com/en-us/library/hh831505.aspx Thanks! – Jaans Aug 22 '14 at 6:12
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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.

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