Formatting an External Hard Disk with Ext4

                                         

# fdisk /dev/sdb

Assuming /dev/sdb is the external hard disk. Use d to delete the partition and use n to create a new partition. 83 is the ID of the native Linux partition.

Them, I use mkfs.ext4 to format the partition with ext4:

# mkfs.ext4 /dev/sdb1

Note that mkfs.ext4 expects a partition as its argument.