You never can have too many backups in place. This is technology and it changes by the minute. A hacker can lay low in your network for weeks just “watching” before they strike. The best backups are not visible to someone browsing your network. Mirroring your backup “drive” is dangerous – because if someone deletes the backup the mirror will reflect the same. Sounds like a good idea when you set this up; but now think about the master being deleted… your mirror… mirrors that! So make sure you have multiple iterations of full restores off site.
