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I'm currently running a first gen. model B as a SMB media server with two 2.5 inch USB 3.0 disks connected to an externally powered USB 2.0 hub connected to the Pi. The Pi itself is also powered with a usb cable from the same USB hub. This worked very well for me for a couple years, but even with all of the hacks I used I'm limited to an impressive 5-10 MB/s, so I wanted to upgrade to the Pi 4.

I finally managed to snag one, and would now like to connect it in the same fashion. This time using a USB 3 hub for the improved speed. But I wonder if this will work. I tried to search for this but I did not find a 100% conclusively matching scenario.

Can I feed a Pi 4B using a USB A to C cable from the charge port(2.4A) of the same hub I connect the disks to and connect the data cable to the Pi? (such as the TP-Link UH720 I see is recommended). I know 2.4A is below the recommended, but I will not connect any other peripherals, disable WiFi and Bluetooth, HDMI, possible underclock,...

I also don't fully understand how the USB backfeed issue works, should I be worried about this in my planned scenario?

Any other concerns that might cause me concern?

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To answer my own question: I bought the TP-Link UH720 to power my Pi 4, connect my drives and everything seems to work as expected and has been running fine for a few days. So my proposed scenario seems to work. To power the PI from the hub I used a simple USB 2.0 A to USB C power cable rated for up to 3A(this one from Ikea: SITTBRUNN) and connected it to the designated charging ports on the hub.

I have noticed a bit of overhead in power with this hub (guesstimating about 1-1.5W extra). Perhaps it is not very efficient in converting from the 12V power adapter it uses. But now everything is powered from just one power source.

Some extra notes: the hub is quite large, and was a bit tricky to integrate in my file server as the combined cables for this setup have to come out at 3 different sides of the hub (data to pi and power on top, high power USB for the pi on the right, USB data on the bottom for disks). It also appears that the disks remain powered on after shutdown, presumably because the hub keeps feeding power. Spinning down does seem to work as it did before during operation(after the tweaks I needed to make to get my disks to do so).

Additionally and not really related to my issue, but more my whole setup: I was able to move from my first gen. model B straight to 4B by having the latest OS already on my PI 1 and by simply cloning my SD card to the new microSD card(using DD), no changes needed at all(apart from now using builtin ethernet, disabling wifi/BT,...).

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The first thing you need is determine how much current you will need, then add maybe 10% or so to that number. If the USB will power that fine, if not you will need to come up with a different powering solution. The backfeed will not happen unless you add an additional supply and it feeds power to the USB on the pi. Power from that would go to your computer ie backfeeding.

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