Today I learned about Lsyncd. Not sure how it ever escaped my radar.
Lsyncd watches a local directory trees event monitor interface (inotify or fsevents). It aggregates and combines events for a few seconds and then spawns one (or more) process(es) to synchronize the changes. By default this is rsync. Lsyncd is thus a light-weight live mirror solution that is comparatively easy to install not requiring new filesystems or block devices and does not hamper local filesystem performance.
Rsync+ssh is an advanced action configuration that uses a SSH to act file and directory moves directly on the target instead of re-transmitting the move destination over the wire.
Fine-grained customization can be achieved through the config file. Custom action configs can even be written from scratch in cascading layers ranging from shell scripts to code written in the Lua language. This way simple, powerful and flexible configurations can be acheived. See the manual for details.
Works really well.