Thanks for pointing that out. I was using a power supply with max 300mA, and a powered multiple USB-port bank is used to connect the HDDs.
I just switched to a 65W Lenovo laptop power supply, with an adapter to USB-C. Now both HDDs show up. I wonder what is the minimum Wattage needed to power the Pi to support multiple storage devices.
It's not that simple. On a 4B having more than 15W at the input does not increase power available to bus powered USB devices. Current is limited by the Pi to a shared maximum of 6W (1.2A@5V).
Your original PSU wasn't rated to supply the typical bare board required for a 4B - that's 600mA.*
I'm surprised your apparently non USB PD laptop supply changed the situation. 65W@5v = 13A. While a PI won't draw anywhere near that, I'd have expected a laptop supply to run at a higher voltage (e.g 9V, 12v, or 19v) all of which will damage your PI.
You might have go lucky. It might be a high current 5V PSU or (assuming it's not a simple 2 pole barrel jack) it might have some Lenovo specifc negotiation mechanism which default to 5V if missing/fails.
Oh, and you won't get 65W to a PI over USB C PD as the connector is only rated for 5A. More than 15W needs voltage negotiation between source and sink and the 4B does not support that.
*: https://www.raspberrypi.com/documentati ... quirements
Statistics: Posted by thagrol — Sun Oct 12, 2025 11:54 pm