Raspberry Pi Forums

I want to use an external USB hard drive.

I have a Raspberry Pi 2 Model B.

Some sites say I need a USB hub in order to power it.

Others say not.

Which is it?

And what about the Pi 3?

Thanks

Irrespective of the model of RPi, if the disk connects and runs reliably without a USB power supply then you don't need one.

The main factors in this are:

How much power does your USB external drive use/need?

How much power can be supplied by your RPi after meeting its own needs and the demands of any other peripheral devices or dongles you have connected?

The play-safe option is to add a power supply, while also adding cost, heat, cabling and complexity.

A USB hub is needed if you don't have enough USB ports, regardless of the Pi model and peripheral power needs.

Separate power is not needed if the peripherals don't exceed the Pi's output. Pi2 and Pi3 are limited to 1.2A (Pi2 needs configuration for that). The Pi PSU must be capable of the total power as well.

Extra power can be provided by a powered hub or direct to the disk. Obviously an unpowered hub won't provide extra power.

Be aware that some peripherals don't like working through some hubs.

kingneil wrote:I want to use an external USB hard drive.

I have a Raspberry Pi 2 Model B.

Some sites say I need a USB hub in order to power it.

Others say not.

Which is it?

And what about the Pi 3?

Thanks

Most 3.5" 2.5" USB drives will work directly connected to the RPi USB. (B+, 2B & 3B)
(3.5" and larger require 12V and 5V)

On the RPi 2B (or B+) you have to add this setting: max_usb_current=1 to /boot/config.txt
(The default current is 600mA. Setting to max gets 1200mA)

The RPi 3B is set to max current (1.2A) by default so no config change is needed.

In both cases you need a minimum 2.5A power supply AND and good quality micro USB cable.

The older original B models usually did require a HUB with external power supply.

Does it not get its power from its own power supply? That should not effect the RPi, you just need a USB port free for it.

If it is one of the oddball drives that draws power from the USB port, then it depends on how much power it takes. If it uses a laptop size HDD (1.5 inch) then it likely draws little enough power to use without a powered hub, if it uses a 3.5 inch or 5.25 inch HDD then I would say it likely takes to much power.

Original poster here.

It is an external HDD that drives power from USB. There is no power cable for it.

It's this one:

https://www.amazon.co.uk/Sony-inch-Port ... hard+drive

Also this one:

https://www.amazon.co.uk/Elements-Porta ... hard+drive

Sony -- According to the power spec it should work on the Pi's power. But:

1) If the spin-up current is too high, it will not work.
2) If your Pi PSU or cables are poor, it won't work.

WD -- Can't find the power requirement in the spec

Both -- Try it and see. You are unlikely to damage anything.

DavidS wrote:...
If it is one of the oddball drives that draws power from the USB port, then it depends on how much power it takes....

They're called portable hard drives, not "oddball" drives. And drawing power from the USB ports is pretty much standard for those; nothing odd about that at all.

The USB 2.0 spec supports 500mA per port, which would be 2A for four ports. However, the Pi2 (and Pi3) supply a maximum of 1.2A for all four ports, so that's significantly less than 500mA per port. If you are just using one portable HDD then you should be fine connecting it directly to the Pi2 (with the config.txt change posted by klricks). If you need to connect more than one, then you'll probably want to get a powered USB hub.

Note that I have successfully run two portable hard drives on my Pi3 with a 5.3V/2.4A supply, but I could only access one drive at a time. Trying to access both together (like copying from one to the other) would result in drive disconnects.