Thank you for the helpful information. It sounds like setting up this type of system is more complicated than just adding drives and software to a computer and calling it safe for backing up my data.
The DROBO is just an elegant solution because it can be set up as a virtual drive (one drive letter) on a network, for file storage, and then it has a double redundant backup. It is deigned so that you can start out with 2 or 3 HDs (internal), pop them into the enclosure, and it just does its thing. If a drive is going bad, it will warn you and move the data to the other drive(s). Also, there is a 10 light indicator for each 10% of storage used. When the storage max is reached, it warns you, and you just pop in another drive. I think it holds 5 or 6 HDs.
But it is in the neighborhood of $600 without the drives.
That is just the price for the enclosure and the 'system'. I thought I could circumvent paying that, but I guess not.
Any further input is more than welcome. Thanks!