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Long file name errors could be happening because of the disk format. The first thing that I would confirm is that the file system can handle long file names.

Sometimes, when I copy my stuff to an external drive, some files are not copied. A message says that it cannot be copied because they have a long file name. I don't understand why this should be a problem and anyway, what can I do since I need to copy those files too? Often it's hard to specify their locality and if they are many, forget about it! Windows 7, 64, but in previous versions, I've had the same problem.

In this excerpt from Answercast #69, I look at possible reasons a drive would not be accepting files with long file names.

Files with long names

The problem is the format used on the external drive.

Realize that Windows (and DOS before it) began supporting only file names with eight characters - followed by an up to three-character extension after the dot. That's why so many of the operating system files are eight characters-dot-three because of simply legacy. That's the only way things could be.

Now, at one point, they added long file name support to the operating system. That required that the disk format actually be changed to be able to handle long file names - where file names could be up to something like 255 characters long with an arbitrary amount of periods, the extension could be any length, and so forth.

Disk drive format

The problem is then that if you have one of these hard drives or one of these external drives that is using a disk format that does not support long file names - well, you can't copy files that have long file names to that drive.

So, what I would recommend you do is:

  • Double-check the format of the external drive that this happens to;

  • And if appropriate (in other words, if all the systems that it might be connected to can support it), convert that drive to NTFS.

Converting from FAT to NTFS

Most versions of FAT will handle long file names. Older versions of FAT do not - and quite honestly, I'm kind of surprised that you're running into this.

NTFS, by definition, will handle long file names. It's a simple "convert command" to actually convert the external drive from one file system format to another.

I have an article on how to convert that. It's a command you run in a Windows Command shell. The net result is that you will have a disk that uses NTFS instead of the FAT file system and then it can use or support long file names.

Long file paths

The only other thing I can think of that might cause you to run into this problem is if indeed your file names are multiple hundreds of characters long - or if the combination of the file folders and the file name exceeds something like 256 or 512 characters long.

In other words, the entire path to a file has a limit on it as well.

So, I recommend you certainly look at those scenarios when it's reporting the error. But if it's happening regularly, if it's happening on one specific device, the first thing that I would confirm is that the file system on the device you're copying to can in fact handle long file names.

Article C6024 - November 12, 2012 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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6 Comments
David B
November 12, 2012 1:34 PM

Some have suggested that disabling the 8.3 file naming on a new Windows installation can improve the performance of the system.

I've worked in some large data center applications and have found this to be true, but typically only when you are creating and destroying thousands of files per second in a server environment, particularly within a single subdirectory - essentially using NTFS has a temporary file store.

Otherwise, no discernible difference in performance.

Vanya M.
November 13, 2012 5:02 PM

Just bare in mind that most external disks are FAT formatted, so they can be recognized by both Windows and MAC-os comps...
If you reformat your external disk to NTFS (which, except other "forward" things, allows you to have files bigger then 4GB - FAT format can't have files bigger then 4GB) - so, although advanced format, NTFS will make your external disk readable by Windows comps only... No Mac!

Mark J
November 14, 2012 2:54 AM

I don't think the older FAT format could be a problem in this case as it would have to be a disk formatted before Windows 95 usually not larger than 100MB in capacity. I've occasionally had this problem with deeply nested folders which exceed 255 bytes. I'd tend to think that is the problem in this case.

Ken B
November 14, 2012 9:47 AM

Vanya -- My understanding is that Macs can, inedeed, *read* NTFS drives. (I just ran into this situation helping a client move a few hundred GB of files from his old Windows box to his Mac, via an external USB drive.)

I agree that it's likely to be a "the full path is now too long" issue, as I have seen that numerous times as well. In particular, we will often save a client's data to an external drive before working on their system. The addition of prepending "\ClientData\[clientname]" to the path as it's being copied will sometimes make the final path name too long.

Vanya M.
November 15, 2012 4:50 PM

Hey Ken B.
- that is good to know if such a thing has came forward! I'll definitly look up the way to make MacOS read NTFS - I am havinng lot of trouble with this issue - working with film, where files are huge, and often need to be transfered from Mac to Win users and vice versa...
Of course, i forgot to be specific - whit my 'MacOS NOT READING NTFS FILES' EXPIRIECE ----- MACs DO INDEED SEE FILES ON NTFS DISK - but ONLY SEE, NOT READ THEM - You can see the folders, file names and types, but when you try to RUN or Copy or READ that file from NTFS- formatted disks, that is where thing stops...
That was my problem... If something changed over last 6 months up to year - great..... Do you knoew if there was some tool for this "operation" or is it simply new "posibility" that came with LionOS or something???

Ashkan
November 21, 2012 2:07 AM

If I am not mistaken, NTFS does a better job with saving file's modification time; since it set the time as GMT format, not locally.

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