Extra sample storage: USB vs SD cards

Ward

I use the EMMC for the OS and application code and I'm looking to add extra storage for samples, somewhere between 16GB and 128GB. It seems I can use microSD cards and (short/small) USB sticks. The storage device will not be hotplugged/removed but the instrument will likely not gracefully shutdown. The storage device will be used incidentally to read samples, and it seems unlikely the user would remove power while loading samples.

As far as I can tell, the data transfer speed on the Beaglebone side suggests USB (2.0 or higher) might be a bit faster.
USB 2.0 HS: 30-50 MB/s
microSD: 24 MB/s
However, both are flash technology, and will probably have similar actual read and write speeds.

The (auto)mounting USB/SD cards process is the same, and for both technologies it is recommended to umount before removing it (or removing power?).

It seems to me that the only difference between SD cards and USB sticks is that SD cards are cheaper and smaller, and USB sticks possibly faster. Am I missing something?

giuliomoro

MicroSDs have to be SDHC, which have a size limit of 32GB. The more recent SDXC standard with larger capacities is not supported.

Ward and for both technologies it is recommended to umount before removing it (or removing power?).

it is recommended to umount before removing the media. During a graceful shutdown that's not required, as the OS will do that. During an ungraceful shutdown (pulling the plug), media corruption may happen. The chance of this happening can be minimised if no writing happens on the device (seems to be your case) and the device is mounted read-only (which can be done by passing an additional ro flag to mount and/or /etc/fstab). ext4 partitions (such as the one used by Linux to boot on Bela) are fairly robust to this sort of problem, but FAT32 is much more corruption-prone, so the above approach is recommended.