I did run into a bit of a snag with regards to USB hubs, though I’m not clear on how much of this is an Apple problem vs. a TS4 problem vs. just the harsh reality of how a Thunderbolt dock works.
TL;DR: my 7-port USB-A hub connected to the TS4 is not fully functional.
To backtrack a bit, I had been running my MBP i9 setup through a USB-C dock and an arrangement of USB hubs, and all was working fine. When I upgraded to the M1 Max, I encountered problems with some of my USB devices not working, which I determined was related to hubs being daisy chained. I was able to fix it by rearranging some things, but I was confused at why the setup worked with the i9 but not the M1 Max, as it wasn’t an absurd number of chained hubs (at the most, a chain of 3 including the dock itself).
I have a somewhat better understanding of it now… I believe the problem was related to the fact that my 7-port USB hub is actually internally structured as 2 cascaded 4-port hubs, along with a couple of my devices (dual-slot SD card readers) being “hubs” themselves. Though I can’t confirm (no longer have the i9), I’m guessing that structure put my setup right at the limit as to how deep a USB chain can go, and I’m guessing the M1 Max for some reason added another internal USB hub at the beginning, which put my end devices over the limit in terms of how deep the chain can go.
So how does this relate to the TS4? It appears that the dock’s internal structure (or the reality of Thunderbolt/USB) adds yet ANOTHER hub layer to my chain. Surprisingly I found that the simple arrangement of ONE 7-port USB hub (which feeds 3 hard drives and 3 label printers) connected to a USB-A port on the TS4 left some of those hub-connected devices unreachable (the first 3 ports on the hub were usable, the next 4, presumably the second internally chained hub, were not). Here’s what it looks like with the USB-C dock:
View attachment 1957892
And here it is with the TS4:
View attachment 1957893
Note that extra “USB3.0 Hub” that’s added at the top, and now the 2 “easystore 25FB” drives as well as 2 of the label printers are no longer visible… that second internally-chained hub in the 7-port hub apparently is the limit as to how long the device chain can be. From what I’ve read, I thought there could be 5 hubs (in addition to the root hub), so I shouldn’t be over that limit (that last “USB3.0 Hub” should be #5), unless that first “USB 3.1 Bus” is actually another internal hub in the MBP and is not the “root”.
This isn’t a showstopper, but it’s mildly annoying. There are enough ports on the TS4 to be able to accommodate my setup despite this (I could have 2 separate 4-port hubs), though the purpose of this particular 7-port hub was to feed these drives and label printers on a nearby shelf with only one cable. In the end, I did find a workaround, which ironically involved ADDING a hub. I found that if I connected a hub (with a USB-C host plug) to one of the TS4’s Thunderbolt ports, chaining the 7-port hub off of that one had the effect of actually reducing the number of "hubs" in that chain compared to connecting it directly to the TS4, and worked fine:
View attachment 1957897
There's still one thing I'm confused about though... is a USB hub limited to 4 ports, or 7 ports? I've searched, and found both answers. Some sources say that there's a limit of 4, and that any hub that has more than that is going to consist of an internal chain of multiple hubs (which is consistent with what I observed with the 7-port hub I was trying to use here, as well as with another 7-port hub I had laying around), but other sources say the limit is actually 7. Is the limit really 7, but it's cheaper for a manufacturer to chain a couple of 4-port hubs together so that's what some of them do?
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