Chiron FS is a FUSE based filesystem which implements
replication at the FILESYSTEM LEVEL like RAID 1 does at
the DEVICE LEVEL.

The replicated filesystems may be of any kind you want.
The only requisite is that you mount it.
No need for special configuration files. The setup is as
simple as one mount command (or one line in fstab).

WWW: https://BSDforge.com/projects/sysutils/fusefs-chironfs/