debian:/# dd if=/dev/mmc of=/dev/null bs=1M count=5 
5+0 records in
5+0 records out
5242880 bytes (5.2 MB) copied, 29.0771 seconds, 180 kB/s
debian:/# dd if=/dev/zero of=/dev/mmc bs=1M count=3
3+0 records in
3+0 records out
3145728 bytes (3.1 MB) copied, 14.123 seconds, 223 kB/s
debian:/# dd if=/dev/zero of=/dev/mmc bs=1M count=5
5+0 records in
5+0 records out
5242880 bytes (5.2 MB) copied, 23.1511 seconds, 226 kB/s
debian:/#