manwilde wrote:Excuse my ignorance, but why is it not a backup?.
If your computer got a virus data could get wiped, and it will wipe both drives. Probably not very comforting to imagine these scenarios :) but -- user error reults in deleting files that shouldn't have been deleted, spill liquid in the computer and electrically wreck both drives, an accident damages the computer ...
My backups are not connected to the computer -- they're in a box. The received wisdom is that if they're spun up at least once a year they won't seize.
The bulletproof backup scenario is to also have a backup off-site.