Yes external hard drives can be backed up using both the standard account and a Briefcase account.
If you are backing up an external hard drive using the standard backup account you must ensure that the external hard drive is connected while running the backup client.
If the drive is not connected the client will assume that the files have been deleted and will mark the online backup files for deletion.
There is a 5TB limit for any single external drive including NAS drives and USB drives.
Posted in: General Questions about BeBackedUp