root@guest:~# time sh -c "dd if=/dev/zero of=ddfile bs=8k count=2000000 && sync"
    2000000+0 records in
    2000000+0 records out
    16384000000 bytes (16 GB) copied, 63.4245 s, 258 MB/s

    real    1m25.469s
    user    0m0.444s
    sys 0m49.267s
    root@guest:~# rm ddfile
    root@guest:~# time sh -c "dd if=/dev/zero of=ddfile bs=8k count=2000000 && sync"
    2000000+0 records in
    2000000+0 records out
    16384000000 bytes (16 GB) copied, 63.326 s, 259 MB/s

    real    1m25.773s
    user    0m0.472s
    sys 0m33.466s
    root@guest:~# rm ddfile
    root@guest:~# time sh -c "dd if=/dev/zero of=ddfile bs=8k count=2000000 && sync"
    2000000+0 records in
    2000000+0 records out
    16384000000 bytes (16 GB) copied, 60.6994 s, 270 MB/s

    real    1m22.672s
    user    0m0.436s
    sys 0m31.678s