We have something like that. Is this the 4-disk noisy stack with the blue activity lights?
Do the lights come on pretty much constantly flashing when you save? Ours do and that's how it works.
You can get more complicated if you want. Ours are configured RAID5. We only get 750G of storage, but we can lose one drive and replace it without kissing off a whole show or damaging any data.
You can also use one of the other RAID configurations to get very much better speed. I think RAID1 or RAID2 lets the system work with two or more drives at the same time--effectively doubling the speed.
Of course that also doubles your chance of flushing your show down the toilet if anything fails.
And they do fail. We had the motherboard fail in one of the stacks. We didn't lose anything but time.
Koz