Some more thoughts about this --

Earlier this week someone posted a reference to a program named
sbackup and unless I'm going blind reading its docs and missed
something, it backups to another partition (or directory) on the
same disk.

If that (single) disk goes belly-up, so does the backup.

What I have for my main web/ftp server (since it's in a colo center)
is a second disk that mirrors the primary disk's root and /usr
filesystems per:

thadlabs bash 22576/22609> df
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/aacd0a 492863 40244 413189 9% /
/dev/aacd0e 273417193 167097358 89914803 65% /usr
procfs 4 4 0 100% /proc
/dev/aacd1a 492863 40244 413190 9% /backup
/dev/aacd1e 265365585 167008098 77128240 68% /backup/usr

That's a FreeBSD system in case the disk names seem "odd". :-)

That's worked well for years and it's easy to recover something.