$ dd if=/dev/zero of=/scratch/cassagnea/tempfile bs=1M count=16384 conv=fdatasync
16384+0 records in
16384+0 records out
17179869184 bytes (17 GB, 16 GiB) copied, 9.14511 s, 1.9 GB/s

$ sudo sh -c "/usr/bin/echo 3 > /proc/sys/vm/drop_caches"
$ dd if=/scratch/cassagnea/tempfile of=/dev/null bs=1M count=16384
16384+0 records in
16384+0 records out
17179869184 bytes (17 GB, 16 GiB) copied, 4.92886 s, 3.5 GB/s