Re: Dealing with slow USB disks, was: Re: Saving environment variables in u-boot

On 2021-Dec-19, at 08:18, bob prohaska <fbsd@www.zefox.net> wrote:

> On Sun, Dec 19, 2021 at 10:03:47PM +1100, MJ wrote:
>> 
>> I would think a mechanical USB is going to pull a "lot" of power when beginning spin-up, but once rotating should be easily powered by a USB hub. Though this would not explain how it works on RPI4 unless the powered hub you're using is USB2.
>> 
> 
> That's what I thought too. I certainly didn't expect the disk to work
> without a powered hub. The Pi4 is a different animal; it has USB3 ports
> and more power available. That the mechanical disk works at all on the 
> Pi3's USB2 ports without assistance is quite surprising. 
> 
> There's a table at
> https://hddfaqs.com/seagate-st1000lm048/
> listing power requirements for the drive:
> Required Power For Spinup: 1000 mA

(I'm guessing they list that as the largest surge current.
But they do not list figures for READ or WRITE activity.)

https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#typical-power-requirements

lists the "Maximum total USB peripheral current draw" as: 1.2A
(so 1200 mA) for the B+, 2B, 3B, 3B+, 4B, and Pi400. The 3B and
3B+ list a "Recommended PSU current capacity" of 2.5A, the 4B
lists 3.0A.

Some keyboards or other such could lead to problems if also
connected at power up: Having both a keyboard and mouse at
power up, in addition to the drive, could be a problem:

QUOTE
keyboards and mice can take as little as 100mA or as much as 1000mA
END QUOTE

So stick to a low total power for your other USB devices that
are to be already connected at power up. You might have to
carefully pick what keyboards/mice/whatever to fit the 200mA
budget that is left --or plug some things in only after the
drive has spun up.

> Power Required (Seek): 1.7 W
> Power Required (Idle): 1.6 W
> Power Required (Standby): 0.18 W
> 
> So far I haven't tried to power cycle the combo, that might not work. 
> Still, it's been an informative exercise. Getting rid of the hub is a
> welcome simplification. The machine is still up after standing overnight.


===
Mark Millard
marklmi at yahoo.com