Usually a drive fails without SMART error... I have seen three smart errors so far (on customer's computers) I put in a new HDD (in addition to the one errorring) and started a HDD to HDD copy... the smart erroring drive failed halfway through the transfer on all three cases...
I would get your IMPORTANT data off of it first, and then replace it...
However, there is one cavet. BOTH drives are erroring at ONCE. so it could be an issue with your motherboard. Can you give us a little more info about your set up, are those brand new drives? how long have you had that motherboard? are there other drives connected to that mobo that are not giving errors? etc...
It is entirely possible for a faulty motherboard, or more likely, a faulty power supply, to cause multiple hard drives to fail at once, or in short succession.