Backup solution for the Drobo

Hello, I have a Drobo connected to my Mac Mini. I use it to hold all of my movies, tv shows and music. Even though the Drobo is good for protecting against disk failure it, it does not protect against data deletion or Drobo controller failure. I have invested a lot of time and money into this setup and would like to know that my system is failsafe. Anyone out there with this information, could you recommend a good solution to backing up all Drobo data: Hardware (another Drobo or alternatives) and Software (time machine vs alternatives).
 
I was thinking about just getting a 2bay enclosure and which would give me a good 4TB of space. I think that would cover me for a while, although I am sure I will max out the 6TB of usable space on the Drobo at some point.
 
As a secondary online/offsite solution I was thinking about signing up for CrashPlan, the multiple computer option so I can backup my macbook pro as well.
 
Thanks for any comments.

You could also use Ubuntu or OpenSolaris with ZFS.