Buffalo HD-PHSXXU2-UC Quick Setup Manual page 6

Macintosh OS 9 Setup
Mac OS 9
In Mac OS 9, the MiniStation will automatically mount on the desktop.
The MiniStation comes pre-formatted with Windows FAT32. Your
Macintosh will recognize this format so you may begin using it
immediately. This format will allow for use on both Macintosh and
Windows computers.
Mac OS 9 will not allow you to reformat the drive to a Macintosh format.
You must use Mac OS X or a third party disk utility to reformat the drive,
if reformatting is necessary.