1 Preparations

copy 16 bytes from /dev/random into a file e.g. sd001.seed:

dd  if=/dev/random of=sd.001.seedbs=16byte count=1

2 Benchmark Write Speed

run

./prng sd001.seed | dd of=/dev/sdXX bs=128k iflag=fullblock oflag=direct status=progress

where /dev/sdXX is the device for the SD card

this should run for a while an write pseudo random data to the sd card

any errors there are a general problem except for when the sd card is full

once you know the number of blocks for the specific sd card

you want to add count=xxx to avoid overrun

dd if=/dev/sdXX bs=128k iflag=direct count=xxx status=progress | md5sum

this will give a read performance and calculate a checksum

the checksum can then be verified with:

./prng sd001.seed | dd bs=128k count=xxx | md5sum

if the checksums do not match, the sd card is not keeping the data written