Is using a single drive a wise move?

I have a single drive MBL; also have an usb 3 harddrive for backup.  The usb 3 drive came before the MBL existed/available.  Now & then I think about a 2nd MBL for use as a backup instead of the usb 3 drive…

Anyway, the usb 3 drive is the backup & “quicker” access (cannot tell subjectively) from the pc.  Have RMA’ed the MBL twice so that the backup alleviates problem of lost data (audio, video docs).  If the MBL was a dual drive in a raid mode & I had ro RMA, everything is lost, twice!. 

Definitely do not want to rip 1300+ CDs again; won’t need to do so with a backup drive of any type, just need to do backups every so often, depending on usage, of course.