Pi4 NAS - insufficient power for 2x HDDs

Hi all,

I have a 2GB Pi4, powered by the Universal USB-C 5.1V 3A supply.

I was planning to run a NAS with 2x 2TB HDDs. Connected via the SATA to USB adapter using USB 3.0 connector.

Problem is that the Pi4 only seems to have enough juice for one of the HDDs at a time. As soon as I plug in the second HDD, they both go into a “insufficient power” mode where they struggle and fail to initialise.

Any ideas how I can get them both working?


Powered USB 3.0 hub?

USB3 spec is 900mA max from each port.
Startup current for external drive might be a touch more briefly so two of them on a 3A power supply only leaves 1A for the Pi i.e. not enough.

Make sure the power unit for the USB 3 hub is rated for at least 2A

1 Like

Thanks neilman.

So, the powered USB3 hub will be the only thing connected directly to the Pi, and the two USB3-to-SATA adapters are connected to the hub?

With USB3 transferring data up to 625MB/s and the Toshiba L200 drives rated at 300MB/s each, it should just work without slowing down.

Yes, the power draw of the hub from the Pi will be very low (just logic power)
Can’t be sure of the speed aspect but from what you suggest it sounds plausible.
Must be worth having a shot with a hub :-)

I may have gone a bit overboard perhaps, but this is what I ordered.


One thing which concerned me is that the “charging” ports on externally powered USB hubs are generally (all?) only delivering power, they do not provide a data connection, which would be bad for me.

I chose the Anker unit (above) because it has a very beefy 5A, 12V delivery from its power brick. I am actually intending that this will be the power source eventually for both my Pi NAS and my Pi OSMC.

i use this one and recently had 5 pi booting from ,all pi’s were running something,with no issues , 3 pizeros,1-pi3b+ connected to the 7 inch official lcd ,and a pi3A+ connected to 5 inch lcd

Yes, I think “beefy” just about covers it ;-)
I think that the charging-only ports feature a “power delivery” system where resistance/voltage on the USB data pins determines the amount of charge to be delivered. So “negotiations with the charger” replace actual data flow.
It is a tad expensive for a “suck it and see” experiment but, if it works, it will work well.

This wouldn’t have worked for me as it is purely a charger. I needed a USB hub to plug in the HDDs, passing on the data connection to the Pi. These data ports on the USB hub also needed to supply enough juice for the HDDs to run (my original problem with the HDDs both plugged in directly to the Pi)

right you are ,I confused myself and the two devices …