I'm testing a pair of sd cards this way:
The first card I did this on (sandisk class 4) gave a write speed of 5.4 MB/s, which is about what I expected based on the results on that page. However, the read speed was 21.6 MB/s, which there are almost no class 4 cards listed that come anywhere close.
The other card (adata class 10) had a (disappointing) write speed of 7.6 MB/s, and an identical read speed, 21.6 MB/s.
I realized the file cache could probably interfere with this, even though that entire file will not fit into the available RAM. So I re-ran the tests, flushing the cache after the write test and before the read test:
sync echo -n 3 > /proc/sys/vm/drop_caches
free demonstrates this is effective.
However, again both read tests are 21.6 MB/s. I've tried rebooting -- exact same thing. The cards contain identical raspbian systems with the stock 3.2.27+ kernel.
Anyone know what is up with that?