This is an oldie, but a goodie. I was reminded of it by a recent incident.
The short answer is that FAT32 has a file size limit (~4GB).
When working with databases on a FAT32 volume, you can get errors like “Database Compactor error: Insufficient disk space” or “Unable to fixup database <db.nsf>: Insufficient disk space”.
Typical example is a mail archive, since these are commonly kept on users’ local disks, which are far more likely than servers to have FAT32 volumes.
Solution: either convert the partition to a file system that can handle larger file sizes, or move the file onto disk that uses the “better” file system (including moving it to another computer, of course). Then open the database, and reduce its size (eg archive documents from it into a second database, delete documents, discard indices, compact, etc). Then warn the user, and present the smaller file(s).