I'd set up a main drive as the OS drive and then get TWO drives of the same size for DATA. I keep all of my data on a drive other than the OS, and mirror them.
What is your exact setup for this? I just had the hard drive fail in my 9 month old Macbook Pro and am looking for a better way to manage my data. Luckly I was able to recover all my data because the computer was able to boot in target disk mode. I do run Time Machine on it, but hadn't run it in a couple weeks when the hard drive failed.
This is in a desktop. For a laptop, like a MacBook, I would get a network drive and send your TimeMachine data to it.
If I only had a laptop I'd run my backups to a network drive AND have an external drive that I'd copy all of my data to every few months and store it off-site.
All backups should have at least 3 copies. The original, on-site backup and off-site backup.
Online options are really good for laptops as well, since most laptops don't have Terrabytes of data.