If you are using a drobo, I highly recommend keeping your backup on regular non-RAID external drives that can be accessed on any computer.
A friend recently had his 6 year old drobo die, and it’s been a little harder than I though to get the drive pack working again. It turns out you can’t just take the drives from one drobo and put them in another drobo and have them work. They need to be compatible units, and use the same firmware. Sometimes that just isn’t possible, so if your actual drobo dies, you could loose access to your data forever.
Fortunately for my friend, the drobo was used for backup, which eased the pain, but it still left his safety margin a lot thinner.
The drobo is a great unit, but you do have to plan ahead for how you you will fix things when they fail. Figuring it out after things fail can be a lot more painful in time, money, and frustration.
As I said above, I recommend using regular external drives for backup. A mac or PC formatted drive is a well understood and supported method of storage, and should work on almost any compatible computer. That comparability makes disaster recovery a lot easier, and removes the need for an exact model/exact firmware drobo to access the data in the even of a major failure.
This is meant to be a KISS recommendation. 99% of photographers are not IT experts and need simple, safe, easy to use, and reliable storage. If you are an IT expert, then don’t nit pick this and feel free to use any solution you want.
And one last thought, 6 years life for my friends drobo is pretty good. electronics don’t last forever and I think he got his money’s worth.