One thing to keep in mind with a drive like this with the choice of either RAID0 or RAID1... RAID0 combines the two drives into one in a way that maintains capacity (so in this case, you get 1TB out of the two 500GB drives) at increased performance (which is not realized in a DVR) at the sacrifice of reliability (if either drive fails, you lose the whole set, so you've effectively doubled the chances of a failure). RAID0 uses the drives "in parallel", such that they each store the same data, so if one fails, you still have the other. This significantly increases your reliability, but it's now a $160 500GB drive.
So unless you are interested in $/GB penalty for doing the RAID1 mirror setup for increased data security, for a DVR you are better off getting a single drive rather than striping two together.