How to Avoid USB Thumb Drive "Disk Full" Errors

Have you ever gotten a "disk full" error while copying files to your USB thumb drive?  Did this happen despite your drive showing plenty of remaining storage space?  The are two possible causes for this problem:

1) The USB thumb drive is bad.  It could be damaged or have reached its read-write cycles limit (USB thumb drives have a finite, albeit very high, number of read-write cycles).


2) You stored the files on the USB thumb drive's root directory and ran afoul of the root directory's storage quirks.

How do you tell which is the problem?  If you see remaining storage space on the device, then there is a good chance that the problem is issue number two, which is fixed easily by following the steps at the end of this post; in my experience a bad drive shows no remaining space.

How to Work Around a USB Thumb Drive's Root Directory Storage Limits

Let me preface the solution with some history.

In the old days file names were limited to a mere 8 characters because of the limitations of the FAT (file allocation table) file system.  The popular portable storage medium of the old days, floppy disks, had 224 slots to hold directory names.  Since file names were short, this seemingly low ceiling did not inconvenience users that often.

With the advent of Windows, the allowable length of file names increased from a paltry 8 to a whopping 255 characters.  (Talk about supersizing.)  Though USB thumb drives are much more capacious than their floppy disk predecessors, they usually use the same FAT formatting.  Why use FAT?  Because there are several advantages:
  1. Cross platform compatibility.
  2. Lower number of read/writes, thus extending the USB thumb drive's lifespan.
  3. Fast.
  4. Decreases the chances of data loss when unplugging without using Safe Removal.
There are a few tradeoffs in using FAT, though, among them being same fixed root directory capacity we saw with floppy disks. When all of those directory slots fill (though the number of slots probably is more than 224, the exact number of slots is hard to determine), you no longer can add more files, even if much of the USB storage device's capacity is unused. Files with long names take up more than one slot, so a USB thumb drive's root drive can fill quickly.

Fortunately it is easy to avoid this issue -- just put your files in subfolders on the USB thumb drive rather than directly on the drive.  The number of directory entries in a subfolder is variable and expandable so the only limitation you will encounter will be the USB thumb drive's storage capacity (which probably won't quite be the stated number, by the way; for example a 2 GB drive might become full at 1.64 GB) .

If you USB drive is balking when you attempt to add files, then
  1. Simply remove some files from it to make it usable.
  2. Next, create subfolders and put all the files on the still on the USB thumb drive's root directory into these subfolders.
  3. Lastly, put back the files you deleted, also into subfolders.
Now your USB drive should no longer complain that its belly is full though it still has lots of room.  If these steps did not eliminate the problem, go out and buy a new drive.

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