(EDIT: somebody suggested this above too, I realized later)
Figure in the time it takes, and the risk that a DVD will not be readable 2 weeks or 6 months from now, and the 2tb hard drives might work out cheaper in the end.
Depends on how much your hourly rate is for swapping DVDs in & out & waiting for the burn.
$80 for a Seagate 2tb SATA, 6gig/second transfer rate. 2 terabytes is a LOT of DVDs. Even the 3tb Western Digital might be cheaper (but those are more expensive per byte than the 2tb)
And of course there's the online backup - I hear backblaze is good
A major benefit of hard drives over DVDs, especially with Linux, is easy RAID.