Too many external disks for a Mac Mini?

den.thed wrote:

3. a cheap or faulty USB hub with a weak or failing power supply

4. or maybe just not enough power to operate all of the drives at the same time

Actually many powered USB hubs do not supply equal max power to all the ports on the hub. They sometimes assume one port will have power supplied by the host computer.

Did you install any of the WD or Seagate software/drivers?

If so, go to the manufacturer website for removal instructions

and get them off your system. No special drivers or software

are ever needed to use any USB drives and will only ever

lead to either an unreliable system at best or data loss at

worse. All they do is fight whatever operating system is trying to

do to work properly.

Barring that, how old are your hubs? it could be one or both may be

failing or may not be up to their specs. One issue I had at one time

were drives suddenly starting to unmount and remount. Eventually

discovered that I had a fault hub.

I don't have 10 bus powered external drives connected to my Late 2012 Mac Mini's all at the same time, but I do occasionally get close to that along with a number of other USB devices. What I do is, use one 7 port self-powered USB 2.0 hub to plug all of my USB 2.0 devices like keyboard, mouse, LG DVD drive, USB 2.0 external hard drives and USB 2.0 flash drives into. Then I have two 4 port self-powered USB 3.0 hubs that I plug my external USB 3.0 drives, USB 3.0 flash drives and a self-power USB 3.0 dual drive dock into.

To be honest, it's going to be very difficult to troubleshoot the problem with so many hubs, cables, drives and other devices. The best advise I can give, is to add another self-power hub, so that you can segregate the USB 2.0 from the 3.0 devices and spread part of the load out to another self-powered hub. It is also a good idea, to plug all of the hubs directly into the Mac Mini instead of connecting them into each other.

FWIW, the USB spec calls for a host controller to allow for

127 connections which includes hubs and endpoints within

devices. That last part as an example means for something like

a typical webcam, which a mic and a camera, those are two

"endpoints" within one device and therefore counts as two

connections. Also, some devices like keyboards may have in internal

usb hub to connect things like a mouse, trackpad, numeric keyboard.

So, that keyboard at a minimum may have two endpoints, the keyboard

itself and the hub and if any other devices get attached they add to it

as well.

With that said, inherently, I would think that inherently that

you haven't reached that limit with your system.

The next, which is unrelated to USB, is how many data drives

can the OS handle. Actually, more specifically how many mounted

volumes can be accommodated. Perhaps someone more knowledgeable

than I may have that answer. And that doesn't really have much to do with

file formats either as the number of volumes is a lower level operating

system function.

No problem here with 11 various external drives connected to my Late 2012 Mac Mini.

The TM 4 backup from the fire safe was updating at the time and I could still navigate around in any of the drives without any slowness or issues.

So with that done and said, I'm starting to think that you have one of the following problems.

1. a bad or weak USB cable somewhere in the mix
2. a bad or corrupt external drive somewhere in the mix
3. a cheap or faulty USB hub with a weak or failing power supply
4. or maybe just not enough power to operate all of the drives at the same time

Wouldn't your configuration be better served with a dedicate NAS instead of all of these drives? I certainly understand the investment you have already put into these, but, for example, a Synology DS918+ with and external drive bay would support up to nine drives. You can still use some of your USB drives for their portability, along with the NAS. You can even connect some directly to the NAS enclosure as well.

If you are going to run that many hard drives at once, then make sure each USB3 hub and each USB3 drive enclosure supports the UASP protocol for best performance.

https://blog.startech.com/post/all-you-need-to-know-about-uasp/

woodmeister50 wrote:

I saw your test and looks good in terms of further

helping the OP. One still wonders, what a limit may be

in the total number of mounted volumes considering the

basic underpinnings of BSD/UNIX in macOS. HFS, HFS+,

and APFS only really define max limits of a volume.

Perhaps in my free time I may investigate that.

There may be a limit on the number of "/dev" entries, but I doubt this limit is being reached here.

I have no idea what the real limit is but I have a 4 drive enclosure which I intended to eventually use as a RAID and haven't gotten around to setting up as a RAID. I also have two 2 drive docks as well as a single external SSD. That brings me shy of your 10 but I've sometimes plugged in a couple thumb drives and micro SSDs so I have exceeded 10. I suspect your hub might be the issue along with too many bus powered drives perhaps.

woodmeister50 wrote:

The next, which is unrelated to USB, is how many data drives

can the OS handle. Actually, more specifically how many mounted

volumes can be accommodated. Perhaps someone more knowledgeable

than I may have that answer.

That's a good question.

While the "someone more knowledgeable" thing eludes me, I'm will be sure to check out the "how many data drives can OS handle" part later tonight when I get home.

den.thed wrote:

woodmeister50 wrote:

The next, which is unrelated to USB, is how many data drives

can the OS handle. Actually, more specifically how many mounted

volumes can be accommodated. Perhaps someone more knowledgeable

than I may have that answer.

That's a good question.

While the "someone more knowledgeable" thing eludes me, I'm will be sure to check out the "how many data drives can OS handle" part later tonight when I get home.

I saw your test and looks good in terms of further

helping the OP. One still wonders, what a limit may be

in the total number of mounted volumes considering the

basic underpinnings of BSD/UNIX in macOS. HFS, HFS+,

and APFS only really define max limits of a volume.

Perhaps in my free time I may investigate that.

I did find a few interesting things in my search of USB

specs and how the actual star/pyramid structure of it

really works.

I could have adding a couple more drives, but ran out of USB ports. Which is probably a good thing, because it's kinda of scary risking everything to try and create a total melt down.