I have a simple task that I am trying to accomplish: attach two USB 3.0 external bus-powered platter-based 2.5" hard drives to a single USB 3.0 port and have them both operate at USB 3.0 speeds.
To this end, I purchased a Mituten USB 3.0 Hub with external power supply. That hub had problems, so I returned it. I then purchased the highly-rated Sabrent USB 3.0 Hub with external power supply.
The Sabrent always shows a USB 2.0 MTT Hub (VID_05E3 PID_0610), and a USB 3.0 Hub (VID_05E3 PID_0616), which is an improvement from the Mituten device.
However, according to USB Device Tree Viewer v3.1.7, when attaching the identical drives to the Sabrent hub, one or both drives seems to randomly get assigned to either the USB 2.0 MTT Hub, or the USB 3.0 Hub. It appears totally random: sometimes it is drive 1 that gets placed on the USB 2.0 MTT Hub, sometimes it is drive 2, and sometimes it is both drives. This defeats the goal of having both drives operating at USB 3.0 speeds.
Am I doing something wrong? Is there a way to consistently get USB 3.0 speeds from two USB 3.0 external hard drives via a single USB 3.0 port?
(Related question on Hardware Recommendations SE: https://hardwarerecs.stackexchange.com/questions/9634/usb3-hub-that-can-handle-2-external-hard-drives-simultaneously)
Best Answer
Yes, you keep buying cheap uncertified hubs with weak power supplies. Mechanical HDDs have a nasty ability to draw substantial peak currents when spinning up and/or during search. Your hub has PSU at 2.5 Amps. The hub has 4 ports, so it must supply at least 0.9 x 4 = 3.6A, plus power for the chip itself (usually 1+ W extra), which would add up to about 4 A. Your AC-DC adapter has only 2.5 A.
The drives (which I saw in the past) can take 1.5 - 1.8 A on spin-up, so it is very likely that the entire 5-V power distribution rail sags, and disrupts USB 3.0 traffic. You need to check inrush and spin-up currents on your HDD enclosures to be sure.
One technical problem with 5-V external supplies is that the normal (2.1/5.5 or 1.3 mm) power jacks are rarely rated for more than 2 A. A reputable 4-port USB 3.0 hub would have a 12-V PSU, with internal DC-DC converters to 5 V for downstream ports. This adds cost. USB-IF certification adds cost to meet. So good hubs are expensive. You get what you paid for.
A good USB-IF certified hub (e.g. Belkin, ) will cost you $50++.