Hello Guys
I just shifted from ST to Hubitat and I am loving it. I have a question, If i attach my ST hub via HubConnect then the ST will process the devices locally or it will still use the cloud? I have a big house of 13000 sq ft (including basement), and I am planing to use multiple hubs. Is it good idea to use my ST 3 hub via HubConnect or should I use multiple Hubitat hubs?
Thank you
Hubitat can't change what ST does. Your ST drivers that are cloud compute will continue to be cloud compute. The conversation that happens between the ST hub and the Hubitat hub is local.
I left ST because of cloud compute drivers so my advice is to ditch ST completely. If you don't mind the outages where you can't turn your lights on or off then you can leave your stuff on ST and HubConnect it. There is no reason to use multiple Hubitat hubs unless you have a specific use case dictated by some (typically zigbee) device.
With love, that is not totally true. I am right now (verifying download) in the process of setting up a 2nd "Apps and Rules" hub to offload some of the custom apps and low priority high chatter rules. My goal is to reduce the amount a work my main hub does so that it can respond to "mission critical" events faster. Custom apps like Device Watchdog, Echo Speaks, Notify Me, Hubigraph, even smartly dashes, and the EmailNotifier, not apps but still could all live on the 2nd hub taking those loads off.
Out buildings or large homes that do not plan to have a single mesh could also be cases for multiple hubs.
But NO none of those are good reason to keep ST. I have not completely tossed mine because I do not love the way HE treats the Spruce moisture sensors I have. It reads as humidity and I don't find them as variant as ST readings were. I have two so I MIGHT turn ST back on to use one on each to compare. But the lawn looks great and I don't even want that bad mojo in my house so...
Like @codahq said unless you have a use case for ST take it out to the wood shed!
Fair points. In future firmwares and even on the current firmware the hub resources can be managed better. I'm trying to level set the expectation that one hub should be the goal.
Outbuildings is a fair reason for a second hub. Large homes can be depending on the how the square footage is laid out, especially if the Z-Wave is the protocol and the device count is, or will be, above 255.
And how could I leave out the Unofficial Ring Connect buy none other....
... and homie has 13,000sq ft. He could put my house inside his house, and I have a decent house! It's safe to say he might have a dead spot or go over 255. First world problems. I do not share your pain. 
If you have a 13,000 sq ft home, you likely could pay someone to run around to turn lights on/off, water the lawn, and secure the premises while you're away. Change their name to "Alex" and you can use voice control.
Seriously I love hubconnect, and keep my devices mirrored to ST, for the app control, and those moments, when i USED to go to work, and wife calls saying this or that is not off, or someone pees on the flood sensor and it shuts off the water, etc.
If you can't cover all your huge space with one hub, get some repeaters and deploy from the hub center outward. You could get another Hubitat hub, as many do, but not necessary. I have a 2nd hub just to experiment with, but without it my mesh is good.
You may find, after discovering all the capabilities and add-ons that you have so many rules and automations, that a 2nd hub might help to smooth things out. This platform is incredible with so many options, you never run out of things to add.
I bought a 3rd hub because I never want to be without one(in case of failure) and to support the amazing job Hubitat has done.
That conversation is cloud dependent. Otherwise I would have put my lights on ST instead of buying another HE.
Which is good for a small space, but much more expensive for a very large one than buying multiple hubs. Good repeaters aren't generally the cheapest repeaters (as we found out with the peanut plugs). Also, in a 13,000 sq ft house he probably doesn't want "wall warts". I think this would be a great place for the new Jasco Zigbee 3.0 in-wall dimmers/switches that should be coming out very soon.
HubConnect v2 has 'enhancements' to a ST connection...
But is still ST cloud dependent, correct?
They can be but if they are in the same network the cloud doesn't have to be involved. Both hubs can doesn't locally. I don't use it though so I could be wrong about how it's implemented. You can tag srwhite or ask in that thread for confirmation. It's probably in that thread already if I had to guess.
What I read was that by using hubaction, the hub bypasses the HE cloud, but still uses the SmartThings cloud.
Local LAN HubActions should be available on either side. The problem I think it's that even though the communication between the hubs is local on the ST side as soon as the app talks to a driver many/most of the device drivers are almost all cloud computed.
Again, I don't use HubConnect but I know that you can send and receive on ST without the cloud. I've written a local integration to a ESP8266 garage door controller on ST and it continued to function without internet.
Instead of going around and around I'm going to tag @srwhite.
Don't be surprised if you don't get an answer til November.
I was using hubaction during the beta, but switched back to http due to it being unreliable/missing commands with keeping a couple virtual switches in sync. I’m not here to bicker, I just don’t want people to think that integrating a SmartThings hub is going to be as fast or reliable as another HE, or several for some of us 
If you look in the logs, you'll see data that looks similar to:
app:582 2020-05-11 09:30:27.311 pm trace Sending httpGet app:582 2020-05-11 09:30:08.322 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:29:09.562 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:28:08.456 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:27:08.636 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:26:08.789 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:25:29.513 pm trace Waiting for http callback response from SmartThings hub... 1/40 app:582 2020-05-11 09:25:28.790 pm trace Sending httpGet app:582 2020-05-11 09:25:28.020 pm trace Waiting for http callback response from SmartThings hub... 1/40 app:582 2020-05-11 09:25:27.278 pm trace Sending httpGet app:582 2020-05-11 09:25:08.195 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:24:08.236 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:23:08.866 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:22:08.233 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:21:08.561 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:20:29.261 pm trace Waiting for http callback response from SmartThings hub... 3/40 app:582 2020-05-11 09:20:28.758 pm trace Waiting for http callback response from SmartThings hub... 2/40 app:582 2020-05-11 09:20:28.255 pm trace Waiting for http callback response from SmartThings hub... 1/40 app:582 2020-05-11 09:20:27.505 pm trace Sending httpGet app:5822020-05-11 09:20:08.277 pm traceReceived ping from ZeeSmart. app:582 2020-05-11 09:18:09.152 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:17:08.226 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:16:09.110 pm trace Received ping from ZeeSmart. app:582 2020-05-11 09:15:30.484 pm trace Waiting for http callback response from SmartThings hub... 2/40 app:582 2020-05-11 09:15:29.890 pm trace Waiting for http callback response from SmartThings hub... 1/40 app:582 2020-05-11 09:15:29.134 pm trace Sending httpGet
You can see that not every communique with ST is successful first try. It's coded to retry 40 times. Yesterday I was seeing it hit 40/40... which I had not seen before.
You can see I'm using HubAction to ST.
On the other hand... my use for ST is minimal... I can go entire weeks without a glance. I do glance several times a day to verify connectivity of the main portion of my Production set of Hubs and ST would standout.. I'm not specifically looking, but I can't help but see. 
Thanks for sharing that. I’m only using it for Echo Speaks, presence, and 2 peanut plugs. Using HTTP connection and usually checking a couple times a day I have yet to see this connection fail. A lot of times in the morning my other HE or one of the Homebridge hubs may say it’s down, even though no issue is apparent. Not sure what to make of it, outside of a bug/misreport.
Download the Hubitat app
