I have a 120TB unraid server at home, and a 40TB unraid server at work. Both use 2 x parity disks.

The critical work stuff backs up to home, and the critical home stuff backs up to work.

The media is disposable.

Both servers then back up to Crashplan on separate accounts - work uses the Australian server on a business account, home used the US server on a personal account.

I figure I should be safe unless Australia and the US are nuked simultaneously.... At which point my data integrity is probably not the most pressing issue.

The stuff that I actually care about are automatically backed up twice, once to a simple external on site and once to a cloud. The cloud rotates between the most recent backups so it never takes up more than 1tb compressed, while the local external keeps backups for much longer (something like 6tb at a time).

Tape or backblaze

So you have 56TB of total storage, but how much of that 56TB is actually used? Take the amount of storage used and add 10-12% to that figure. Now you create a new NAS (preferably off-site) with that amount of storage and that becomes your backup target. Take an initial backup (locally if possible to speed up the process) and then you can use something like rsync to create incremental backups going forward. This is the method I've used and so far it has worked out well. I target 10-12% more than the amount of used storage for my backup capacity because my storage use grows reasonably slowly. If your usage grows faster you might want to increase your "buffer" a little more so that you're not having to constantly add drives to your backup target.

A second offsite NAS (my old one) with the same capacity for the larger files

Backblaze B2 and a Hezner storage box for Really Important stuff.

I switched to a DAS for my storage and use backblaze to back up all 50TB+. I couldn’t find a cost effective way to do it with a NAS.

Definitely following this

I don't for media. I have 2 parity drives and that's it. I'd like to do some kind of off site mirror but I haven't had time to figure it out and buying enough storage to do that is expensive.

My actual data for like taxes and stuff is backed up to my server and backblaze.

I've started using k8up to save my photos and config to an encrypted restic repo in an s3 bucket. having a lot of trouble backing up my SQL DB though, not as easy as they make it sound.

Zfs send. Done