But these solutions don't provide rapid access to the backed-up
data in the event of a major disk crash (e.g., if a centralized home
disk bites the dust, leaving everyone on the system unable to work).
What you want here is an instant slot-in replacement, and for this,
rsync is an excellent option.
rsync doesn't keep historical data, but if all you want is a
nightly current snapshot, it does that very well. You can use a "proper"
backup solution for your historical data.
Either set rsync up onto a disk that you can physically slot in to your
regular or another server; or use a spare machine that can be plugged in
immediately instead (e.g., by changing your NFS mappings). Set up a
cron job to synchronize nightly, and you're done. In the event
of a serious main server crash, just slot in the new disk and get everyone up
and running again with only 24 hours of data lost which if your backup
schedule permits, you can then recover at leisure.
Be aware that although this will work if the main disk crashes overnight as
rsync will not be able to access it so won't run it will not work if
something more subtle goes wrong. In this case, both disks will have corrupt
data, and you're back to using your normal backups for a regular restore.