I recently decided to replace the SD card in my Raspberry Pi and reinstall the system. Without any special backups in place, I turned to rsync to duplicate /var/lib/docker with all my containers, including Nextcloud.
Step #1: I mounted an external hard drive to /mnt/temp.
Step #2: I used rsync to copy the data to /mnt/tmp. See the difference?
Step #3: I reformatted the SD card.
Step #4: I realized my mistake.
Moral: no one is immune to their own stupidity 😂
In my experience, flash drives are way more reliable than SD cards and I’d put SSD and HDD above both of those.
I wish they’d just ditch the SD card on the Pi already as it’s always the most likely reason why your stuff stops working. For my Pi running Home Assistant, I’ve swapped to an SDD as the boot drive. For the others, I still use SD cards but they’re just doing basic stuff like running Klipper on my 3d printer or a (WIP) live photo frame that can be easily swapped with a replacement SD later.
It really depends how you define reliability. SD cards are physically nigh indestructible, but can show failure when overwritten often. Hence for one off backups it’s actually a good alternative. It will start showing problems when used as a medium that often writes and overwrites the same data often.
I would recommend backups on SD cards in an A/B fashion when you want to give a backup to someone else to store safely.
Reliability in that I’ve used flash drives and SD cards for years but have only ever had issues with corrupt SD cards (probably at least half a dozen times) while I’ve never had any with flash drives.
Constant writes is an issue with them, which is why I think it’s stupid that the Raspberry Pi Foundation continues to use them as the default storage/OS drive. Then again, they continue to make insane choices with power supplies as well, so it shouldn’t be a big surprise.
I really wish they’d just give us an m.2 slot on the back