My i5 Farmer with 16GB RAM only connect 200 HDD by 40 JBOD HDD Closure, I use 16 USB data hub, and cannot add up more than that, I have to use shared network
Yes as I wrote in my post yesterday there is the USB endpoint limit which is completely hardware dependent. Since must investigate itself what its hardware supports that is impossible to say in general.
And there is the tier limit of 7 which is prescribed by the USB protocol.
You will probably have reached one of these limits.
But since the fewest have exact knowledge of this, they only reach the limits because they have not distributed their devices optimally on the existing USB roots and have linked their USB hubs unfavorably.
Normally you can probably connect even more if you distribute the devices optimally. with regard to USB enpoint limit and USB tier limit.
What about using USB hard drive enclosures, such as the 10 bay Icy Box (https://icybox.de/en/product.php?id=301). Would that distribute devices more optimally?
I’d love to go the easier route of getting JBOD’s, but sadly I don’t have the luxury of having a dedicated server room so noise level will be an issue.
It depends on how the hard drives are connected internally on the hardware side.
If they are connected via SATA controller and only the enclosure is connected via USB to your system, that’s fine. Because so only very few endpoints and only 1 USB tier is needed.
But if the HDDs are connected via USB HUBs and then connected to your system you need at least 3 USB Tiers and lots of USB endpoints (with USB3 at last 66).
So it all depends on how the hardware side of the case is designed.
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Just to clarify what you have said. The addressable limit is per USB Root / chip connected to a PCIe bus. Most motherboards (or maybe all) have only one USB Root chip.
However, by adding PCIe USB cards, additional USB Roots / chips can be added, thus the actual limit can be increased.
Yes
U can also change the USB protocol from XHCI to EHCI if your BIOS/mainboard and OS supports it. Then all USB devices will run with USB 2 and need only half as much USB endpoints as USB 3.
Or you can use a USB 2 cable in front of all USB3 devices and HUBS which will then automatically run with USB 2 only and also use only half of the endpoints.
But the Tier 7 limit can probably not be changed as far as I know
no, most have more than 1. only the very cheap and smal one have 1 or 2.
in Linux ucan use:
lsusb -t
this will show u all ur Root HUBs, Hubs and USB devices.
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Cool.
A quick question about XHCI vs EHCI. Looking at my old AMD APU board, there are those two entries:
/: Bus 08.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 480M
...
/: Bus 03.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/4p, 480M
Looks like one root is already set to run in XHCI and the other in EHCI. However, both are marked wit 480M, what I assume is the xfr speed. Would it mean that changing that protocol will only change which protocol is being used, but the speed will be the one supported by the physical chip (e.g., will not drop to USB 2 level)?
Yes
XHCI supports USB 1/2/3 and EHCI only USB 1/2, but since these are only protocols, the root USB chip decides which USB max speeds can be used.
If the chip only supports up to USB 2, only USB 2 is reached even with an XHCI protocol.
As already correctly recognized, your two root hubs only support 480M, so maximum USB 2.
edit
Using EHCI with a Root USB 3 will also drop to USB2 speed, because of the max USB2 supporting by EHCI.
Yeah, that is an old AMD e-350 chip, and there are also few USB1 roots on it, but also one USB3 (5G).
Maybe to rephrase my question. Assuming that the chip supports USB3 (5G) and runs in XHCI. If we change the protocol to EHCI (USB2), will only the protocol change accordingly while the speed will still be at 5G, if connected device is USB3, or the max speed will be dictated by protocol rather than the chip phys capability?
Yes
i realize this point of u to late 
only max usb 2 speed with EHCI.
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USB2 workds perfect and destroyes thse limits with easy. plus you can add additional USB host controllers easily.
