I think there are two main factors contributing to the wear of the SD-Cards:
- Number of write cycles
- Environment temperature
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.