Nothing says that you can't own two external drives if your data is worth a lot to you. Use one as the ultimate backup safely left at home in a dresser drawer most of the time.
That way if the computer goes bizarro and trashes its internal drive and the external one while connected, you still have a fairly recent full backup in the dresser drawer.
Probably best SCANDISK the internal drive and normal external drive before connecting the ultimate backup to the system. Have only one external drive connected to the system at any given moment - if you want to be doubly careful.
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