Initially when getting setup on Hubitat I assumd I needed two hubs so that my zwave could cover the full house (6k sq ft, pretty spread out) without having devices doing 4 hops, so I have this extra C-7 just sitting in a box collecting dust. But I found that most everything just works fine with a single hub.
Lately I've noticed that intermittently we see things not work or respond super slowly and I can't figure out whether this is possibly zwave versus just hub performance.
We use Hubitat as the command and control center hub for all of our various other interfaces. We have Google home hubs throughout the house along with an Alexa in the guest bedroom and we're an iPhone house so we have a Homebridge server running on a separate Pi.
What I'm trying to figure out is the answer to "When does it make sense to split services out across multiple hubs using the mesh capability?" - I can't find any clear guidance and would love any input.
Device wise, what I have is:
122 Zwave devices (35 are Fibaro Window Sensor 2 devices that don't repeat)
23 Zigbee devices
1 Hue Hub w/ 4 lights
App wise, I have:
Amazon Echo Skill
August Home
Basic rules (8)
Google Home
Google Home Community
Homebridge (tonesto)
Mirror Me (6 mirrors)
MyQ Lite
Rule Machine (6 rules)
Switch bindings (1 binding - used to be 7 but I found mirror me to be a lot more reliable)
In an effort to reduce IO I turn off description text logging & debugging on nearly everything... still last week I for the first time got a "CPU Usage Too High" warning from the Hub so I killed a couple of apps that I no longer needed and the CPU usage went back to normal.
So with all of that knowledge, I'm trying to get some guidance on whether moving some apps/devices into a mesh makes sense. As well, I'm trying to figure out whether it makese sense to split my z-wave network out... I could put the additional Hubitat C-7 on the other side of the house so that I have multiple controlllers.
This is all going to be a big PITA and an entire-weekend project so I'm also trying to figure out whether it is worth the effort.
Am I pushing the limits of the C7 or are there people crazier than me who have put way more devices & apps into a single home hub?
If things worked okay, I would tend to recommend leaving it as is, but if you are starting to see issues, splitting the Z-Wave network would be a good idea. Hub Mesh works very well to keep everything in synch.
Also, even though the standard supports in the 230 range, it is recommend to keep Z-Wave at the 50 range. So with 122, you are probably pushing the hub and mesh to their limits.
Agree with @Sebastien, but the high CPU warning has me wondering if something else may be happening also. Do you have any devices that look to be accumulating CPU at a high rate?
The milliseconds are CPU time used in servicing the device and so can be used as a measure of the device’s impact. Not an absolute, but may provide something to explore deeper if severly skewed.
In my opinion, device count is a simple stand in to the real limiting factor and that is: the number of packets on a mesh. It seems like every device in the ZWave Plus era are able to pump out vast levels of data..
That's a bathroom fan & light dual relay device. I understand and love that the device IS CAPABLE of sending power data, I just don't need it and disable seems to be a rarity in manufacturer's offerings. I can't use it in this bathroom since On/Off tells me exactly the same as how much power is in use.
To the hub, it doesn't matter that it's not used. The Status comes from the device and it has to be parsed to determine Keep? or Discard? Thus the hub's just as busy processing junk as good stuff (in the Z-device arena. Clearly good stuff then gets thrown against rules for further processing.)
I have 5 ZWave meshes in my house this moment and ZNiffer isn't indicating anything odd. I wish we could get a number out of the hub along the lines of packets per second... but we do have Logs: Device and App with each having a % of total column.
That is a good first step. Those can devices paired at S0 or S2 security that don’t require that level of encryption.
I would only move apps that use devices that are mostly/all on the new hub.
My personal far future plan is to get a 3rd hub that will host all apps with the other two taking care of all devices. I currently have 2 where one has most of my devices and apps, and the other has problematic/processor intensive devices or apps.
Wow, 50 is such a low number. Is there any caveat when you consider powered vs battery?
Last year I bought 20 Zooz zwave leak sensors. I haven't installed all of them yet but they'll definitely put me over the 50 quota.
I do have a Smartthings hub with some zwave devices and a Home Assistant Blue (still need to install the zwave combo stick). Would you recommend distributing any new devices among the other hubs to avoid any performance issues?
I use hubconnect and Hubitat/Smartthings integration in Home Assistant to bring all the devices/automations together.
It would be really great to get some official guidance from the Hubitat team, surely they have some data about how many devices can be supported.
Also I'm with you Alex in that battery powered (non-repeater) leak sensors that just call home occasionally but aren't polled or part of the repeating network surely must be lower usage.
Given the number of permutations of devices, drivers, and applications that are possible I don't expect to see this as the exceptions to any statement would ultimately invalidate the statement.
One clear example where it solves a problem is where you have two distinct and separate areas that you want to control where the radio signals don't overlap at all. Something like a house and a second building some distance away (e.g., a separated garage perhaps).
As an example where it could cause more problems than solve is if you have two meshes where the radio outputs from the hub can overlap. In this case, multiple hubs can transmit at the same time which would increase the chance of packet collision / packet error. Basically, each hub would be using the same set of channels so you don't pick up any extra bandwidth since you can't do overlapping transmits on the same channel, but you do pick up extra chances for collision (though the radio units implement protocols (CSMA) to avoid collisions). In this case, a single hub will inherently better coordinate transmits as it can't overlap its own transmits on the same channel.
Another thing to remember, at least since Z-Wave 500 series, each device can simultaneously listen on up to 3 channels, so single hub has up to 3 x 100kbps of transmit using different channels - that's actually a whole lot of bandwidth for home control as the packets are very small.
You sound knowledegable about zwave. Do you have a number of hops after which you see problems? I've got a number of devices that are taking 4 hops because the house is large.
Somewhat knowledgeable (at one point I had worked as a radio / cellular systems engineer - its been many years since I did that, but still have interest in understanding how things work).
The maximum number of hops in zwave is 4 (I think). I have not had a problem even when a device hits that limit.
If you have a lot of devices with 4 hops, try relocating the hub (is it in a central position?); avoid a closet or other place where the signal must immediately pass through walls / brick / metal.
I agree. I have been over that number for a while and have 3 Z-Wave meshes running in the same home. It mostly works well, but I do see issues with one mesh interfering with the others at times.
I just bought two more c-7s while they were on sale yesterday and my plan is to go all in on this idea. Since this is going to be a huge overhaul on my setup I wanted to plan and do this right so I don't have to redo anything.
I got to thinking about specific apps like Motion Lighting. If you put that app on the third hub won't there be additional latency since it's communicating over the network before performing the automation?
My specific plan is to split my device hubs into Upstairs and Downstairs. If I'm setting up a motion automation with an Upstairs sensor and Upstairs light shouldn't the app reside on the Upstairs hub in order for it execute as fast as possible?
I don't think you will notice any latency.. I like having multiple hubs. By location is great - I had a setup similar to yours (1st floor / 2nd floor) but then switched over to by type (Z-Wave / Zigbee / Cloud & Network) because I had some C-5's in addition to a C-7.
Another thing I've done is move all my logic from HE to Node-RED running on an external server. It really seems to reduce hub overhead and I get more control over the resources.
Thanks for this input. I really wish I knew Node-Red but that is still on my to do list of things to learn. I do like the simplicity and flexibility of a lot of apps such as Motion Lighting.
I didn't think about splitting by z-wave and zigbee but my network is growing, particularly my zwave mesh. I'm afraid putting them all on the same hub will overwhelm it, especially after I add 20 more leak sensors (non repeating).
Maybe I should fire up a wave Poller just to keep it warm. 
