I have a 2TB NAS (LaCie D2) that I think just failed. We store our pictures and other documents on there. We'll take it to get the data recovered, but any ideas on how we can back up files (about 800 gb or so) reliably?

I have a 2TB NAS (LaCie D2) that I think just failed. We store our pictures and other documents on there. We'll take it to get the data recovered, but any ideas on how we can back up files (about 800 gb or so) reliably?
Hard drives don't last forever, and I have a Blu-ray writer, but the blank Blu-ray disks I have are only 25GB each. Perhaps buy two 3TB external drives and have redundant backups to go with the NAS (when we get a new one)?