File size on disk is much larger than the file size

[agundrum]

I have a LinkStation Duo Pro.  It has two 500GB drives and the drives are mirrored.

I've been trying to figure out why the file size on disk is much larger than the actual file size. For example,

Size: 135 KB (138,633 bytes)
Size on disk: 1.00 MB (1,048,576 bytes)

Why is there such a discrepancy?  Can this be fixed?

Thanks!

[Texturtle]

What OS is running on the computer you're checking from?

[agundrum]

Windows 8.1

[Texturtle]

Very interesting. I just looked at an LS420 from both a Windows 7 and Windows 8.1 machine and the Windows 8.1 reports wildly inflated size on disk numbers while the Windows 7 unit reports actual size and size on disk numbers that very close, if not identical. I would expect size on disk to be a little bigger in some cases because of the way file systems work.

This is a reporting error between the NAS and Windows 8.1.

Do you have another system you could look at the same files with?

[agundrum]

Yep.  Windows 7 Pro SP1.  Results are wildly different but better aligned.

Size: 135 KB (138,633 bytes)
Size on disk: 136 KB (139,264 bytes)

[Texturtle]

That's actually about right. Keep in mind that all file systems use clusters. Here's a pretty good explanation:

http://en.wikipedia.org/wiki/Data_cluster

What is boils down to is that the extra kilobyte you're seeing is actually empty space, but it can't be used for anything else because part of that cluster is in use by this file.