My current design is the motion sensor and almost all plugins run on the “Main” Vera unit, the light switch on the dedicated “Z-wave slave” Vera unit. All devices added to the "Z-Wave slave’ unit are bridged to the “Main” unit and can be controlled from the Main unit’s UI. Device control from Main-Z-Wave Vera’s are fast. Status updates from Z-Wave–>Main take 2-5 seconds if used to trigger scenes or events from the Main Unit. Due to this delay and alot of plugin devices (Hue lights) needed in the scene…I need the motion sensors on the same unit as the Main automation engine.
My “Main” Vera 3 Pro unit has all my plugins (Russound Home Audio, Somfy Blinds, Philips Hue, OpenSprinkler, Nest, Weather Undergorund, and Logic Plugins like SmartSwitch) and majority of automations. For Z-Wave devices, it only 26 devices consisting of 3 locks, contact sensor & garage door opener contact, 10 scene controllers (in wall and remote) and 10 interior motion sensors on its network. Averages .60 CPU idle load with 79k of memory available.
The “Z-wave” unit (Vera Lite) has 75 devices consisting of 25 Leviton light switches, 7 wall outlets/lamp modules, 3 sirens/strobes , 10 cameras, and security 23 sensors (window shock sensors, window/door contact sensors) water leak, outside motion, perimeter doors). It only has the MIOS Update plugin, System Info, and Z-Wave Unit Info Viewer plugin. This unit is in a more secure internal location along with the internet modem w/4G and battery backup. Averages .40 Idle CPU load with 33k memory available.
I would have put 100% of the Z-wave devices on the Z-Wave unit but couldn’t for optimization purposes. The motion sensors we’re moved to the main unit to cut down on scene execution lag so audio and Hue lights would lag on motion being sensed… Locks we’re added as the Vera Pro is right next to all the locks, and they can be fickle. Also, the main unit has 50% of my home lights with the Hue Plugin (which is very quick BTW, typically faster than the Z-wave devices) which is why most automations run from there.
I have not had remote actions take longer (main unit sending on/off to slave), actually they seem quicker on my network. However, sensing that a switch has been manually shutoff has a delay of 1-2 seconds before it hops from device → z-wave slave unit → main unit. Since motion is my primary firing method on and off from the main unit, having the switches delay reporting back that it was manually turned off isn’t an issue for me. It just takes 2 more seconds for the bathroom TV’s and fan to sync off once the main light is manually turned off for example.
Running plugins like ‘Smart Switch’ using a bridged/slave switch didn’t work for me. Also, installing the ‘Combination Switch’ on the slave caused the main unit to reboot every time the switch goes off or on.
For a large network, and if you architect it right where your pushing commands to your slave unit vs polling/receiving updates, bridging works well.