I know this is a noob question, but I am a noob just starting out.
I am running HA on an older 1U Sunmicro Server. It only has USB 2.0 ports on it. I wanted to start adding zigbee support to my HA server so I ordered the SONOFF ZB Dongle-P. However, I noticed it is USB 3. Now, I know many devices are backwards compatible, with some trade offs. However, this is a radio device and many are not backwards compatible. So, will the SONOFF ZB Dongle-P work in a USB 2.0 port? I have dug around on Google and some say yes, but with a loss of range. Others say no. Since HA users tend to have more experience with this kind of thing (as most are DIYers like me), I figured the smartest thing to do was ask the people who would most likely have the same experiences as I do. What have you all experienced?
AFAIK usb version (leave usb C aside) differs mainly for supported speed. There may be also the amount of power available.
I haven’t studied much on this so take your caution…
In my view for an RF adapter neither speed nor power settings will be a problem. Testing it wouldn’t cost much…
Between USB 2 and USB 3 the difference is speed and power available. You are correct there. Hence why I am concerned. If there isn’t enough power, the radio wont function. If there isn’t enough data speed, then the device may not be able to communicate with HA.
For the superficial reading I’ve done “dommestic” rf network speed are in the range of few hundred of kbps, under 1Mbps.
Some order of magnitude below usb2 speed (for speed I think even usb1 would suffice).
For power I seriously doubt that a zigbee adapter could max out the 2.5w a usb2 port is able to supply.
And if even if this should happen you could easily solve with a powered usb hub.
Don’t worry, it will. Actually it’ll work in your favour because USB3 causes RF interference with zigbee ( read this).
Hell, I would personally still put it on a USB2 extension cable just so I would move it away from the server chassis and ensure that I’d be getting the best signal possible. Snake that cable out of the rack too (if you’re using one), so that your coordinator will get the best possible signal.
I actually have ceiling mounted a powered USB 2.0 hub that I will be plugging the dongle into. My sever is one of several in a metal rack enclosure. I learned in college that grounded metal boxes are REALLY good at blocking RF Signals ((Faraday cage)) so, I wanted to get the dongle outside the box. Then I have a 6 foot USB cable from the hub to the server ((which I moved to the top of the rack to have the shortest run)). Wife is not happy about the 6 foot rack standing in the living room, but gotta start somewhere, right? LOL
Yeah, too bad no one has invented a Faraday cage for wives’ complaints so far 
Joking aside, I don’t think you really need to have the USB hub on the ceiling. I don’t even think the hub needs to be powered if you’re not plugging in a bunch of other devices in it.
Somewhere on top of the rack should be sufficient, provided you’re not in a multi-storey house and that the server location is relatively central.
Given you’re just starting out, I’d do the wife a favour and try it out on top of the rack first, then monitor the zigbee network for a month or so. Just remember to add at least one zigbee router in each room to avoid mesh issues.