Hello - I currently have a C5 (all zigbee devices) and a C7 (all z-wave devices) with integrations and automations on both of them.
Ideally. I'd like to combine everything on a single C8 Pro, but I don't know if it's possible to append devices and apps when doing a migration or if you have to replace everything existing on a hub.
If the latter, that would suggest that once you have split your network across two hubs, you're pretty much stuck that way forever unless you want to recreate everything manually.
If I can't merge what's on the two hubs, I'm thinking I'll go with two C8s rather than one C8 Pro.
You cannot combine hub database or radio backups from multiple hubs.
But:
This is not the case. You can still restore one complete, working backup, then manually migrate/add your other setup to this hub (all at once or piece by piece, however you choose; Hub Mesh should make this pretty easy to do at your own pace). I would pick the hub that is the least amount of work to migrate as the hub you don't start with, but either way should be a lot easier than starting everything entirely over. Some tricks may make this even easier:
If you don't have both Zigbee and Z-Wave on both hubs (i.e., if you are currently split with only one on each), you can probably first migrate your Z-Wave hub, the migrate your Zigbee hub.
This will result in "stranded" Z-Wave devices, i.e., entries in the Z-Wave Details table that the radio database knows about but the hub doesn't, but a "Discover" from the table should bring them back. I have not tried this in a while and don't know if it's really that simple anymore (biggest thing I can think of is you'll need to wake sleepy devices when doing this), but it seems like it should still work. And even if there are still a few devices you need to re-include for whatever reason, that is easier than everything.
You'd also have to manually add back any apps/automations on your Z-Wave hub (and put the devices back into them), as you'd only have the hub database from the most recently migrated hub, and your apps are part of this database, which again, cannot be merged.
Regardless of how you do it, you can export apps from one hub and import them to another; this process also offers a device replacement feature, so as long as the device you want is on the new hub, you can just select it when importing, then it should work as before. This is a lot less work than manually re-creating every app on the new hub, though it can certainly work, too.
I did something similar to the above when I combined a C-5 (which did mostly Zigbee and lighting automations) with a C-7 and then C-8 (which did Z-Wave and almost everything else) into a single C-8 Pro a couple years ago. I'm pretty sure it was easier than doing everything manually, but YMMV based on your specific setup, as is often the case.
Since your Z-wave devices are on your C-7 hub, I would recommend migrating that over to the new C8-pro hub. You will then have to migrate the devices on the older C-5 hub manually, one at a time. Zigbee devices will need to be reset to factory and then paired with the C8 Pro hub, but the Zigbee pairing process is usually simpler than pairing Z-wave devices.
Make sure you save copies of all the rules on the C-5 hub as they will have to be recreated on the new hub. That might involve doing printouts of the rules.
One thing you might try is moving devices and rules from the C-5 hub over to your C-7 hub before upgrading to the new C-8 Pro, but this might be just as much trouble as doing it the first way suggested.
I would suggest to migrate the devices needed for the rule to the new hub before importing it because the import process will ask what device is associated to each old device from the exported rule. This is easier than selecting nothing and then having to go back and change everything in the broken rule.
Also export all rules before removing devices as these will be broken and then if I remember right, it's not possible to export a broken rule, at least in my memory of last doing it when I separated the two buildings on my property to two separate hubs in preparation of building the new house.
