4e9fe054_Implementing_a_backup_strategy_able_1___BACKUP_DEVICE_OPTIONS_Target_backup_device
[Advantages] Easy Reasonably fast (6) Files not lost if master drive crashes or becomes unbootable Drive containing backup can be disconnected easily so that it is then completely isolated from possibility of infection by malware Drive can be stored in a safe location or off-site If the backup is a clone of the master drive or a bootable partition from the master drive, and the PC's BIOS supports booting from a Firewire device (very few seem to be able to do that), it may be possible to boot the PC directly from the drive in the enclosure. (11) [Disadvantages] Cost of hardware If the enclosure is fan-ventilated it could be a tad noisy (7) (but in my view, having a fan in the enclosure is essential if the enclosure is used for more than 30 minutes at a time) Most PCs are unable to boot from a backup drive in a Firewire enclosure. If the enclosure has both Firewire and USB interfaces it is possible that this disadvantage can be avoided if the PC can be booted using the drive connected as a USB device.(11), (12) [Target backup device] 
Drive in an external enclosure that has a Firewire interface to the PC
Implementing a backup strategy
Target backup device