Buffalo HD-PHSXXU2-UC Quick Setup Manual page 5

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.
Macintosh OS X Setup
You may choose to format the
drive with a Macintosh format.
This is recommended if you do
not plan to use the unit with
any equipment other than
Macintosh computers. To
format in Mac OS X, Navigate
to your Utilities folder and
select the application Disk
Utility.
Select The Buffalo Hard Drive
and click the Erase button.
Follow the wizard to complete
the format process. Click
Erase when done.
NOTE: Formatting the drive
will erase all data on the drive.