Maximum number of supported USB devices on MacOS? (Non-theoretical)

[lifereinspired]

Hello,

I’ve been researching and searching all over for a year now trying to find this information. I’ve even contacted Apple support and they didn’t know the answer.

I need to know the maximum number of supported USB devices on MacOS. I know the theoretical maximum is well over 100 but I’m looking for the actual number. Does that number change if the devices are external hard drives (fully powered externally & not relying on USB at all for their power).

I keep running into issues where devices won’t show up once I have a certain number connected but that number seems to change somewhat (it’s not always the same number). I don’t know if I’m running up against a maximum number that‘s set and hidden somewhere in MacOS or if it’s a issue with my Mac. Apple support was totally useless. The closest info I found was regarding a Hackintosh that gave a command that lifted the USB device limit but that didn’t seem to make any difference on my Mac mini.

Any help would be greatly appreciated! Thanks so much.

 

[bogdanw]

The maximum number of connected USB devices is dependent on the total power they need.
Apple: "How many devices can I connect?
Multiple devices can receive high power simultaneously until the extra power is consumed. If further devices are connected requesting additional power, they will default to the maximum the port allows or the device will not function until the original device (or devices) using the extra power is removed."
https://web.archive.org/web/20170115133810/https://support.apple.com/en-us/HT204377

 

[Slartibart]

I keep running into issues where devices won’t show up once I have a certain number connected but that number seems to change somewhat (it’s not always the same number). I don’t know if I’m running up against a maximum number that‘s set and hidden somewhere in MacOS or if it’s a issue with my Mac. Apple support was totally useless. The closest info I found was regarding a Hackintosh that gave a command that lifted the USB device limit but that didn’t seem to make any difference on my Mac mini.

Besides was @bogdanw already wrote - additionally issues can arise when mixing devices with different USB version: e,g. a hub might change the transfer protocol to the version (and speed) of the lowest USB version connected. As a result all connected and even cascaded devices will run slower or will not mount reliable (or at all) because e.g. the USB3 device, you want to connect, detects that the connection provided by the hub runs for whatever reasons at USB 1 - which comes which a much lower power, therefore the USB 3 device might not reliable mount. Or the total cable length is beyond the supported limit for the USB version, et cetera, et cetera.

Best to provide details of your usage scenario so someone here might be able to help: hardware, macOS version, USB device and versions, cables, etc..

Otherwise asking "Maximum number of supported USB devices on MacOS? (Non-theoretical)"” is like asking “How much trees are in a forest? (non-theoretical)” 🤓

 

[Fishrrman]

OP:
"I keep running into issues where devices won’t show up once I have a certain number connected but that number seems to change somewhat (it’s not always the same number)"

The "maximum number of devices that can connect" means nothing in your case.

What DOES "mean something" in your application is "how much BUS POWER are the devices you have connected consuming?"

If you exceed the amount of bus power that the Mac can provide, it will start dropping devices or shut USB port(s) down altogether.

SOLUTION:
Get a POWERED USB hub/dock.
The hub/dock will supply the required bus power, and the Mac won't become "over-loaded" and "shut down the bus"...

 

[Kathleen13]

Late to the party but other searchers may come here. Some of these answers do not seme to understand the question properly or at least do not speak from experience, IMO. I do have experience here, but no exact answer but I can tell you the problem is not as simple as it seems. I have a macbook Pro 2019. I have 3 powered USB 3 hubs, each connected via adaptor to one of the 4 USB-C ports on the Mac. Each hub has 7 ports. I have 18 USB 3 drives from 8 to 18TB each.Half of those are backups pf the others so I do not keep them all mounted normally. Most of the time in fact only 7 are mounted. I can tell you from experience that, using several different well reviewed powered hub models over the years and different models of Macbook Pro and versions of OS, if you try to fill all the hub ports with drives you will have trouble keeping them all mounted. This should have nothing to do with port power as the hub is powered and the drives are powered. You can also have trouble just from having too many drives total (e.g. 18) even though none of the hubs is full. This is why even when running backups I have my backup program mount the backup drives as needed and dismount each before moving to the next drive. I also keep my 2 less needed drives dismounted. I rarely have trouble with 7 drives distributed across 3 hubs and really 9 would fine. The cut off is unclear as it is not consistent behavior. I just play safe. The idea that you can just use powered hubs and powered drives and all will be well is false. That said If you are having an issue with just keeping a few drives mounted, maybe you have a bad hub or cables

 

[bogdanw]

macOS and the 15 Port Limit
"only 15 possible ports per controller"
"USB Hubs attached to one of your USB controller's ports have a different kind of port limit. In total, a single USB port can be split into 127 ports. This includes USB hubs attached to USB hubs"
https://dortania.github.io/OpenCore-Post-Install/usb/#macos-and-the-15-port-limit

 

[appa14]

macOS and the 15 Port Limit
"only 15 possible ports per controller"
"USB Hubs attached to one of your USB controller's ports have a different kind of port limit. In total, a single USB port can be split into 127 ports. This includes USB hubs attached to USB hubs"
https://dortania.github.io/OpenCore-Post-Install/usb/#macos-and-the-15-port-limit

This might be a stupid question, but I hope someone can help me clarify this: Are there Mac's with multiple ''USB Controllers'' so the max amount of Ports is not 15 but 30 for example (when the Mac has 2 controllers, or even 3 for 45)? Or am I thinking the wrong way and does a Mac always have just one USB Controller, and therefore a limit of 15 USB flash devices connected at once? Thanks for any help on this.