We are concerned as SD cards seem to be the weak point of Raspberry Pi based gateways.
Is there a reasonable alternative for this?
@andreas found this recently:
https://www.westfloridacomponents.com/blog/use-f-ram-replace-sd-card-raspberry-pi/
We are open for ideas. It should work easily also in outdoor environments and should be at a reasonable price (remember a Raspi costs € 35,- so a solution > € 100,- will be too much).
I think there are two main factors contributing to the wear of the SD-Cards:
F-RAM tackles only Problem 1, as it will be used as RW medium, while the SD-Card will be used read-only then. It doesn’t solve Problem 2, but it will add another component to the gateway, that may fail at some point.
Since the vast majority of write cycles on the gateways is related to logging (and ocassional updates ofc ;), we could get rid of this huge wear-contributing factor by enabling centralized logging, while disabling local logging(*) on the gateway itself.
(*) disable all local logging except security related stuff like logins, etc.
The second problem is iirc, that we are using consumer grade SD-Cards on the gateways, which are probably not as durable (no. of write cycles/environment temp.) as similar industrial/military grade cards.
A brief search for example brought up Apro SD-Cards, where the controller as well as the Flash storage itself is industrial grade: https://www.amtron.com/micro_sd_card/APRO/PHANES-F_slc_microsd_datasheet.pdf
These cards are no performance wonders (approx. 25MB/s read and write) but they include a wear-leveling mechanism and a bigger temperature range to operate within (-40°C to +85°C).
If the price fits our expectations, we could try these kind of SD-Cards in one or two of the new gateways and see if this could be the solution to our problem.
there are options like these:
http://www.suptronics.com/miniPCkits/x850_v3.0.html
But i’m also not sure if it makes sense to use cheap hardware and try to make it better by adding stuff and moving the weakest link to another point in the chain. There quite likely are better quality, possibly less performant (which likely would suffice as well) options which are more durable as a whole. Though i have no idea what is planned to be running on this.
concerning F-RAM - i’ve got a clone of the Adafruit 256kb somewhere, planned to be used on an mcu-based weatherstation… briefly researched before ordering, but didn’t really find bigger versions on the ‘open market’, so i doubt there are reasonably priced options to get.
Thanks for your thoughts on this!
To what @marcus wrote: I don’t believe we are in trouble in terms of performance. As the system boots up it has very limited performance requirements (in this area and in general - it just forwards small packets).
We have good experience with Rasperry installations (running for years on other projects and 1+ year with OpenIoT) but a regular weak point seems to be the SD card. We would like to mitigate this as it might take days or longer until we can replace on same Gateway locations (some are not accessible (by car) during winter, other are mounted on roofs where nobody wants to step on during winter). The idea discussed in the Member Meeting is to find a simple way to improve resilience; if the complexity gets too high, we should skip it and keep it simple (and just replace on fault).
LgS
maybe a RAM-drive would suffice?
Probably. Any persistent storage capable of holding a minimum of 4 GB (8 GB better though) will do.
Do you have a link or experience with such a solution?
We will soon make a larger order and could also get something for testing if we know a specific product that could fit.
Danke,
LgS
as mentioned at the last meeting, there might be an alternative to the classic raspi that could tackle this issue: the CM3+ comes with up to 32gb eMMC. and being designed for industrial applications there might be even more advantages, besides these are promised to be available at least till 2026…
official announcement/blog: Compute Module 3+ on sale now from $25 - Raspberry Pi
The eMMC Flash device on a Compute Module is more reliable and robust than normal SD cards, so it is more suited to industrial applications.
of course a custom board directly combining concentrator and this module would be really cool… 
slightly related:
from the company formerly known as resin.io
in short:
I boot my Raspberry Pi 3 from a USB stick attached to it, specifically the Sandisk Cruzer Fit 16GB, since only a few USB stick models are known to work flawlessly. Instructions on how to boot from USB are provided.
Additionally, I converted partitions with high read-writes, such as /var/log, to tmpfs (RAM disk). Plenty of instructions available on the Internet, like this one.
This Raspberry Pi is used as a control unit for my network storage, so the LEDs on this one are blinking 24/7. It’s been roughly 2 years now and I never had any problems with faulty sectors.