RPI3 swap experiments

[Trev]

 > Mark Millard wrote on 01/07/2018 16:42:
> > On 2018-Jun-30, at 7:53 PM, bob prohaska <fbsd at www.zefox.net> wrote:
[...]
>> It just crossed my mind that the successful -j4 buildworlds that used
>> USB swap (both mechanical and flash) separate from /usr and /var placed
>> the swap  on a powered USB hub.  It would be exceeding strange if that
>> proved helpful, but as things are going....

> Power issues have been mentioned before in this exchange, but it can be
> more like what one might notice with a oscilloscope than with a Digital
> Multi-Meter. If the device sometimes (even very briefly) requires more
> than the rpi3 provides (voltage or current) the device will likely
> fail sometimes despite a DMM not showing anything interesting. The
> same device might work fine on a powered hub that always provides
> sufficient voltage and current (on all time scales involved).
> 
> I've had these sorts of situations before. Without a proper set of
> instruments to monitor for power problems with, it is a pain to
> figure out for sure if such is what is going on.
> 
> So I tend to use a powered hub for USB storage.

My RPi2B is connected to a pocket router via ethernet and USB for power, 
and thence wirelessly to the wifi router at the fibre NTD. The pocket 
router kept getting corrupted settings and losing connectivity. So I 
replaced it. Same thing with the new one. I finally figured out that it 
was a USB power issue - adding `max_usb_current=1` in the config.txt 
file to double the current from 600mA to 1.2A fixed it.

I hadn't considered power to be an issue for the RPi3B+ - it has a 3A 
PSU (limited to 2.5A by the RPi's polyfuse) and does not need the 
config.txt tweak as it already supplies up to 1.2A by default according 
to an RPi Engineer:
https://www.raspberrypi.org/forums/viewtopic.php?p=930695#p930695

Admittedly, I haven't been watching when "out of swap" occurs to see if 
the red power LED goes out momentarily. However, since replacing the 
2.5A PSU with the 3A one I've not seen any red LED fade outs which used 
to randomly occur with the 2.5A PSU.

I'm currently -j4 compiling with an external USB hard drive connected to 
a powered hub, so when that finishes, I'll add the USB memory key for 
swap to the hub and see if it makes a difference.