View source for SD Card Performance Benchmarking

=Preparations=
Note: Be aware that this will wipe/erase all data on the SD card we are benchmarking, also be extra careful to select the correct device/mount point to not wipe you PCs internal drive instead by accident.

get this http://vserver.13thfloor.at/Stuff/prng.c and build it with "-O3":
 gcc prng.c -o prng -O3

copy 16 bytes from /dev/random into a file e.g. sd001.seed:
 dd  if=/dev/random of=sd001.seed bs=16b count=1

=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:
 <pre class="code">15923412992 bytes (16 GB, 15 GiB) copied, 1415 s, 11,3 MB/s
dd: error writing '/dev/mmcblk0': No space left on device
121549+0 records in
121548+0 records out
15931539456 bytes (16 GB, 15 GiB) copied, 1415,66 s, 11,3 MB/s
</pre>


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

once you know the number of blocks (for theabove example: 121548) specific sd card you want to add count=xxx to avoid overrun
 ./prng sd001.seed | dd of=/dev/sdXX bs=128k iflag=fullblock oflag=direct status=progress count=121548

=Benchmark Read Speed=
 
 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 iflag=fullblock | md5sum
if the checksums do not match, the sd card is not keeping the data written