I have a core file server that has a 9TB RAID-Z array in it. This server uses key-based authentication to connect to all of my other hosts - my desktop, VPS, work systems, etc and uses rsync to copy any changes to a locally maintained copy. It also attempts to back up laptops, if they are left on overnight.
Every night this system also reaches out to a remote system in my office that has an 8TB RAID-5 array. It "pushes" any changes, again using rsync, to this remote host. This time it uses the --link-dest argument to create nightly "snapshots." If a file hasn't changed, it simply gets hardlinked. This backup volume is also encrypted, and only the core file server has the key to decrypt it.
For the remote system, I have a script that runs periodically that purges backups according to my own specification. Right now it keeps unlimited yearly backups, three years of monthly backups, six months of weekly backups, and 14 days of daily backups.
Once a month I also run a script to back up the core file server to an external 8TB hard drive, again with --link-dest, creating snapshots. This hard drive is stored in a fireproof safe. It is also encrypted.
I have various levels of redundancy elsewhere, too. (Yes, RAID/redundancy is not a backup). For example, my desktop system has a RAID1 array in it.
In 2000, I installed Windows ME on my desktop system. It corrupted my hard drive somehow, and I lost all of my work prior to then. In case you can't tell, this scarred me for life, and I have worked hard to make sure it cannot happen again.
I'll add, every single storage device that I use is encrypted. Sometimes it's just with a key stored on a separate boot disk (usually an SSD). The rationale being if I ever have to RMA a disk, I don't want the manufacturer to be able to see any of my data.
On another tangent, the remote system mentioned above is actually a rather old GX260 with a SATA expansion card and 3 4TB disks. The boot disk is an ancient EIDE 40GB drive. I keep it around mostly for entertainment at this point. Here's why:
9 Power_On_Hours 0x0012 001 001 001 Old_age Always FAILING_NOW 123756
That's right, the drive has been spinning for a little over 14 years.
Unfortunately I've recently hit a problem where e2fsck runs out of memory (it's a 32-bit CPU, so only 2GiB per process) checking the file system. I tried setting a scratch file, but that bombed for some reason too. So, I may finally have to upgrade the thing to a 64-bit system.
Oh well.