How is this thing? I'm looking to buy one, but they are quite pricey. I have a Drobo to store all my stuff already, but I want something that is bus-powered for one-the-go; this will be used strictly for traveling. Is it bus-powered? And is it a good choice? Also if the HDD inside dies, do I replace the drive myself or do I have to send it in? Also if I buy says the 500GB model, is that with 2x250GB drives or 2x500GB drives? Thanks.