$ diskutil eraseDisk ExFAT GHSRobert-256 disk2s1
A volume was specified instead of a whole disk: disk2s1
Specify a whole disk, or instead use diskutil eraseVolume to erase a volume on a specific partition
$ diskutil eraseDisk ExFAT GHSRobert-256 disk2
GHSRobert-256 does not appear to be a valid volume name for its file system
$ diskutil eraseDisk ExFAT GHSRobertMBASidecar disk2
GHSRobertMBASidecar does not appear to be a valid volume name for its file system
$ diskutil eraseDisk ExFAT Test disk2
Started erase on disk2
Unmounting disk
Error: -69877: Couldn't open device
$ diskutil eraseVolume ExFAT Test disk2
Started erase on disk2
Unmounting disk
Error: -69888: Couldn't unmount disk