Disk defragmenter finds non existent files

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When I run disk defragmenter on Windows XP it's moving files that do not exist. I mean I search the hard drive (including search for hiddens files, etc.) and I can't find the files. Does anyone know how this can happen?

Posted 5-Nov-13 3:42am

ed welch

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Sergey Alexandrovich Kryukov 5-Nov-13 10:13am

It means that you could see the names of the files. Why would not tell us what are they?
—SA

ed welch 5-Nov-13 13:13pm

For instance, "a0197618.exe" and a bunch of similiarly named ones

Sergey Alexandrovich Kryukov 5-Nov-13 13:51pm

And you don't know what is that? Well, there could be different reasons, but it could be a file you were not aware of. In my answer, I explained a more fundamental reason: you always have some files not visible to you as a user, no matter what privileges you might have.
—SA

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Sergey Alexandrovich Kryukov · Answer 1 · 2013-11-05T04:06:00

This is explainable. The files may actually exist, but you never see them as a file system user.

In any file systems, there are areas on disk which serve as internal "system" storage needed to support functionality of the file system itself. For a trivial example, in FAT file system such storage is FAT, "File Allocation Table".

The design of NTFS is different. In NTFS, technically, such areas are also files. They are called "system files", but "system" not in the sense of OS, in the sense of file system. In particular, it has Master File Table (MFT) and MFT records. And each of MFT records is a real file, with its file name. You can see their names below:
http://www.ntfs.com/ntfs-system-files.htm[^],
http://www.ntfs.com/ntfs.htm#basics[^].

From the standpoint of the file system user, they are not file at all, but technically, they are. And they are generally involved in the defragmentation, that's why they the defragmenter can show them to you.

—SA

E.F. Nijboer · Answer 2 · 2013-11-05T03:59:00

Solution 1

What files do you mean? Defrag doesn't move files, it only moves data that belongs to the files, compacting the files.

Good luck!

Posted 5-Nov-13 3:59am

E.F. Nijboer

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Sergey Alexandrovich Kryukov 5-Nov-13 10:09am

Sorry, not true. Files can be moved, too, it depends on how the disk is defragmented, and its initial state. And it does not answer the question. And yes, there are files which can be defragmented but never visible/accessible from the user's standpoint.
Please see my answer.
—SA

E.F. Nijboer 5-Nov-13 10:55am

Nobody would ever defragment a disk if files were moved. It would mean for example that after defragmentation your vacation pictures would suddenly be in some other directory then where you left them. It would be very annoying.

Sergey Alexandrovich Kryukov 5-Nov-13 11:19am

Perhaps we did not understand each other. I did not mean moving files between directories. (This would rather be considered "renaming", which of course does not happen.) Of course, by "moving" we mean physical moving of files, relative to disk clusters. I don't believe anyone could possibly mean changing directory structure...
—SA

E.F. Nijboer 5-Nov-13 16:21pm

I'm sorry, but a file is simply data that has a name, called a filename. Also, windows uses renaming. On unix/linux you have the mv (move) for both moving and "renaming" (just a move in place). I think the discussion could go on for a while I would technically say that files are about file descriptors for accessing the data without any regard of how the data is stored. De-fragmentation is getting the data back together on disk for better access (only mechanical disk by the way because there is no need to defragment flash or ssd drives). Just my view on it, therefor moving files means something completely different to me than moving file data that is scattered all over the disk.

Nelek 5-Nov-13 11:37am

Another way to explain what Sergey says could be:

Have you ever defrag a hard drive? In XP was pretty easy to follow with the colours of the preview and the current status. Did you see the red lines/blocks? That was a file that was saved in different parts of your HD. When the defrag ends, there are less red lines. So in a strict point of view the data of the files are partially moved to stay together in a narrower area of your disc.
Moving a file from one dir to another doesn't implies moving the file in your disc, it implies the information of that file is shown to you somewhere else. But the disc manage it with the full path, without having to move the data of file itself in the disc (or at least not always). Another thing is if you move between diferent drives (USB to HD, HD1 to HD2 or similars), then both things happen simultaneously

E.F. Nijboer 5-Nov-13 16:36pm

Lately I haven't touched defrag because ext4 doesn't need it and flash/ssd drives don't either. As above, a file is simply data with a name, called a filename. Defragmentation doesn't move that, it moves the data of the file so all the used disk sectors are nicely sorted for fast and easy access. The red/blue blocks you see moving is file data beeing moved. The data structure with the filenames (with some other information) is simply kept in place and going nowhere except for updating the location of the first data block, because it is almost certain it will move during defragmentation. I actually know very well what defragmentation is and how it operates on disk level. Also, there is no need to explain the separation of file and data when moving file from one directory to another. That's actually the whole point. In the case of defragmentation it is just the other way around, data is moved, the file is kept in place.

Nelek 6-Nov-13 6:46am

Sorry, your first comment was a bit ambigous, that's why I tried to explain it simply. Just a missunderstand.

E.F. Nijboer 6-Nov-13 10:30am

Just as I thought, but it ended up a nice discussion :-)

Nelek 8-Nov-13 4:30am

Yes, you are right, and still better... I learn a bit more about this subject :)

ed welch · Answer 3 · 2013-11-06T03:37:00

Solution 3

Actually, I figured out what it was. They were files in the "System Volume Information" folder, which stores restore information

Posted 6-Nov-13 3:37am

ed welch

Disk defragmenter finds non existent files

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