See this post by Curt for information.

If your external hard drive is formatted as FAT32, it would be better to reformat it to NTFS.

It has been more than a year since I bought my external hard drive and did the research to use it correctly, and I had forgotten about the formatting business. Curt’s post gave me a flashback. (Thanks, Curt.)

Of course, if you do reformat your hard drive, that ERASES EVERYTHING on it. So first you would copy everything to some other location (like a hard drive on another computer) — and then do the deadly reformat procedure.