I was writing to an SD card this evening from a Mac Book Air internal card reader and the performance reported was 1.4 MB / sec. I later read tested it on the PI and got 20 MB / sec. It is a class 6 card and neither of these figures sound realistic!
I am using
dd for my tests. I hope to revert soon with read and write tests on both the Air and the PI.
Results of identical tests of both read and write on both computers.
PI: read 20MB write 11MB.... AIR: read 3MB write 1.4MB
Using these commands:
sudo dd if=/dev/zero of=/dev/mmcblk0p3 bs=1M count=400
sudo dd of=/dev/null if=/dev/mmcblk0p3 bs=1M count=400
This indicates that the perceived anomaly was in fact lousy performance of the integrated Mac Book Air SD card reader! Makes for very slow image creation.