use usb flash drive as boot disk and swap space

[ryan-williams]

having a pi powering a desktop GUI with chromium or firefox (#7) showing grafana…

…seems to eventually (≈12h) use the default 100MB swap space (on the SD card) and freeze the whole pi.

This results in some data loss, since one humidity sensor is on that pi (the others buffer data correctly since #2).

This may go away with #16, but in general I probably want a story for at least one pi to power a monitor+browser+dashboard, and some good swap space would help.

There are pi-knockoffs on the market with up to 4GB memory, which I can investigate if I get desperate, but I don't think it should come to that.

[ryan-williams]

• pi only supports usb 2.0 (60MB/s), so a lot of SSD's speed (700MB/s) is overkill
• a class 10 SD card like the ones I've been using is 10MB/s, so USB 2.0 speeds are still a huge improvement
• USB flash drives seem preferable to SSDs:
  • easier to set up (1); SSD requires:
  • mSATA SSD (1)
  • some way of mounting to the pi:
    • USB-SATA cable
    • storage expansion board
  • should still saturate the USB 2.0 bus, providing ~6x speedup vs SD card
• with 1GB of RAM, 1-2GB of swap are the recommended sizes (1, 2 (w/ discussion of dphys-swapfile), 3)
• booting from a 64GB flash drive w/ 2GB set aside for swap sounds ideal
• I bought this USB drive to attempt this

Other notes:

• apparently some USB 3.0 devices aren't correctly back-compat w/ USB 2.0 (1), but 3.1 should fix issues
• sample cmds for swap-{partition,file} formatting: 1, 2, 3
• mixed msgs about USB-flash-drive-swapping being good vs bad; seems like it is relative, and will be a strict (6x 🤞🏻) improvement over swapping to SD though

[ryan-williams]

I switched the influx and grafana servers to a Raspberry Pi 3 B+ booting from a 64GB USB drive with a 2GB swapfile:

Haven't tested running a long-tenured Grafana webapp client on it yet, to test graceful degradation to using swap (cf. #16), but will reopen here if further issues arise.