Don't most modern SD cards contain some wear leveling logic?
I did a bunch of research on this a while back and the conclusion I found was: yes, but buy name-brand better rated cards to avoid cheapo cards that do not do wear leveling or do it very badly.
It's nowhere near as good as SSD drives, but it's better than just a naked flash chip... unless I'm wrong.
Hey if you see this can you answer one more question:
How much abuse was your high availability product delivering to these cards in terms of writes? Was it something like a video recorder, database, cryptocurrency, or some other application that did large amounts of write I/O?
I ask because we're about to ship something that uses SD cards, but the I/O is very low. It's a network appliance and doesn't do anything locally that is high write throughput.
The Linux kernel in raspbian treats the SD card like a normal block device. I'm not aware of any special optimization for write wear leveling at the OS level, or on the board's sd card controller.
SD card wear-levelling is usually supposed to be handled on the controller inside the SD card. SD cards aren't like having raw access to flash, you basically write over SPI and the controller in the SD card decides where to actually put it.
This talk about SD cards is really great and explains some of this:
