Things that are deliberately not covered in this answer: How to do a back up and discussion of proper disaster recovery procedures such as physical security and keeping multiple copies in multiple locations. Archival as it is the subject of the preservation of tools and platforms not specific files or formats.
Optical media of any type (Bluray, DVD or whatever) is not suitable for backup of any significant volume of data. Instead my recommendation is to store everything and store it on harddisks or via an off-site (cloud) service available from a few USD/month.
My full backup set (which does include some other similar content) is presently in the order of 3Tb and is not what I'd consider large were I shooting in any kind of volume so I'll use it to illustrate.
At those volumes, the cost of media is around 2.4p/Gb for Blu-Ray, 2.7p/Gb for harddisk and 3.9p/Gb for DVD. But that isn't the whole story - now price up your loss of earnings / time for these two workflows.
Optical media workflow
Set up a disc (decide what files to include etc), label, burn and store it (without scratching or getting any mucky fingerprints on). Your files won't exactly fill each disc and there is an overhead for the file system, on my setup I'd put that at something like 120 BD discs.
The first problem is that it's going to take a while. Lets get a rough estimate that a 25gb BD-R disc needs about 20 minutes to burn. It needs a further 20 minutes to verify the data is correctly written and that drive-time is the only overhead if the operator can organise the next disc to start burning immediately after the current one finishes. That gives you 12 discs produced per 8 hour working day and you need 120 discs. That's 10 working days to produce a backup, minimum.
While you could use multiple burners each one needs a big slice of the available bandwidth of wherever the source data is stored, making it difficult for other work to continue with that store and it is hard to interrupt or slow down to get some work done during that time.
On top of that you are tying up a person who must be paid to nurse a BD-writer for those 10 days (or loss of earnings whichever you prefer). And that's if all the discs pass validation... which is unlikely.
In the event of a major failure you then have to do all that in reverse - even with the best optical media case copying them off means that you're going to need a reader going at full-chat for something like 5 working days.
But writing and restoring the backup to optical media is only half the job since it is unreliable in practice. You also can't be sure that a disc hasn't failed since it was last verified which means the whole set needs to be checked fairly frequently in the hope that hope that there have not been dye-rot issues and (as I've seen) the burner has not produced discs that could only be read back from the burner they were created on rendering the backup useless.
To do it on DVD single-layer would put you in a position that hi-def video source files may not even fit on a single DVD, but you also jump from 120 to around 700 discs to process.
For almost the same cost as the write-once media you can get a bare harddisk of the right size (around 2.7p/Gb for a 3Tb model) and a drop-in reader for SATA devices.
To set it up you need about 10 minutes at most to set the backup running and then you can forget about it while it gets on with it.
Verifying is just as easy and any data loss in the case of a harddisk will be significantly less than removable media (in my experience).
Since the costs are about the same there's no need to reuse the harddisks if you don't want to - although it will save cash if you decide to reuse a disk.
The additional costs are something that can be borne, it can run unattended (overnight for example) and they're a lot more convenient to store in multiple locations (they even come in a nice polystyrene padded box if you want to ship it offsite.)
Backing up an reasonable volume of data to optical media is a Sisyphean undertaking which is not remotely cost-effective.
note: prices sourced December 2014 from eBuyer.com and are for comparison only.