I take system disc images with dd, from Ubuntu booted with a live CD. One of the steps of the process is to mount the drive where the backup file is to be stored. To do that I need to know the format of the drive.
My problem was that
fdisk -ltold me that the destination drive was HPFS/NTFS, which was wrong. Connecting the drive to a Windows machine made it clear that it was formatted as exFAT.
Ubuntu does not support the exFAT format in its current distribution (at least not in 11.04), which explains why
fdiskgave the wrong information.
If you have trouble connecting an external drive to your Ubuntu install, and
fdisktells you it is NTFS, read on...