On 2019-03-27, Roby  wrote:
> A. Dumas wrote:
>> I got a Seagate 1TB external 2.5" hdd for ?50, usb-powered by the 3B+ Pi
>> without problem, that's with the RPi official 2.5A adapter. WD is fine,
>> too, I'm sure (or some will say better). You can set "max_usb_current=1" in
>> /boot/config.txt to double the available power via usb, but that wasn't
>> necessary for me.
>
> Thanks @A.Dumas for the info
> But from the site www.raspberrypi.org I read these RPI technical
> specifications:
> "The USB ports on a Raspberry Pi have a design loading of 100mA each -
> sufficient to drive" low-power "devices such as mice and keyboards.
> Devices such as WiFi adapters, USB hard drives, USB pen drives all
> common much more current and "........." The maximum power the
> Raspberry Pi can be used is 1 Amp. If you need to connect to the USB
> device that will take the power requirements above 1 Amp, then you must
> connect it to an externally-powered USB hub"

I use several "WD - Elements SE Portable Hard Drive" and an older WD
Pi-Drive. All have just a USB connection, and are powered by that USB
connection. They work fine with a modern Raspberry Pi. I even have one
working with an old Pi 1 B+.

My only concern is that they are appear to be designed for occasional use,
not for being on all the time. Even so, I use one in my always-on home
server, a raspberry pi 3B with a WD USB drive. It's been working for
nearly 18 months. My backup server is the Pi 1B+ with a large capacity WD
USB drive.

These disks are mostly sold for external backup or portable storage. The
disks inside are 2.5" drives and take maximum, roughly, 0.5A of current,
which is well below the 1A max for the Pi USB total current. I have not
succeeded in using 2 such drives on a Pi - the Pi doesn't boot. The in
rush current on start up is too much.

I think you will find the general performance of the Pi will be a better
with a USB connected hard drive or SSD. The speed of the SD card interface
is not brilliant.

good luck.
Jim

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