We recommend Samsung or SanDisk cards with A2 or A1 rating. Make sure that it is “Sold by Amazon.com” or else it could be a fake card. Samsung has been the most reliable in our experience with over 50 different MicroSD cards models.
We do not recommend any other manufacturer because they have consistently proven themselves to put out unreliable products.
Our images are designed to detect silent MicroSD card corruption and lengthen MicroSD card life.
If you suspect data corruption, run sudo dmesg | grep mmc and look for errors. Feel free to post your output below if you are not sure what counts as an error.
To test read speed, run sudo dd if=$(findmnt -nvo SOURCE /) of=/dev/null bs=1M iflag=direct status=progress. Press Control+C to end. If this drops below 20MB/s, we recommend another card.
To test write speed, run openssl enc -aes-128-ctr -pass pass:"$(dd if=/dev/urandom bs=128 count=1 2>/dev/null | base64)" -nosalt < /dev/zero | dd of=test.file iflag=fullblock oflag=direct bs=1M status=progress. Press Control+C to end. If this drops below 15MB/s, we recommend another card for best experience.
For unpowered long term archival on the order of a decade, all flash storage devices will lose data. For applications that are expected to run for years, we recommend endurance or even industrial MicroSD cards. These MicroSD card internal controllers will fresh data cells periodically if powered and offer higher reliability.
There’s a power cycle issue due to how the SD card handles VDDIO that we are in the process of fixing. It should be fixed/mitigated in the next firmware release.
Either will work fine. Brand and legitimate supply chain matters more than XC or HC. HC means it’s most likely FAT32 formatted out of the box while XC means it’s EXFAT formatted. Neither matters since you are flashing a new image onto the card to replace the initial data on the MicroSD card.