Windows – does “Size on disk” vary when “Size” does not with the same set of files

filesystemshard driventfswindows

I understand why "Size on disk" is larger than "Size".

I have three NTFS-formatted drives with the same exact data on it. Their allocation unit is 4096 bytes. The number of files and folders as well as the size matches on all three.

However when I open the properties for the root folder of these mirrored drives, only on the first two have the Size on disk match though. On the third, it is slightly larger.

Is this a potential signal of file corruption, or a mere byproduct of the file system?

Best Answer

It is possible that on one system some files have been modified or had a byte changed and so one or more files were moved into or out of the MFT area (where cluster alignment is not used and it may not count towards the filesystem "in use" count) or were fragmented, causing a difference in used space.

From Blackbagtech

DATA ATTRIBUTE

This MFT attribute contains information about where the data for the actual file exists on the volume.  As you may know, sometimes if the data is small enough the entire data of the file can be stored within the Master File Table.  However, in most cases the file’s data is too large to fit within the MFT.

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