root@-2015:~# time dd if=/dev/zero bs=1024 count=1000000 of=/1Gb.file conv=fdatasync
1000000+0 records in
1000000+0 records out
1024000000 bytes (1.0 GB) copied, 6.62436 s, 155 MB/s
real 0m6.737s
user 0m0.076s
sys 0m1.680s
root@-2015:~# time dd if=/1Gb.file bs=64k |dd of=/dev/null
15625+0 records in
15625+0 records out
2000000+0 records in
2000000+0 records out
1024000000 bytes (1.0 GB) copied1024000000 bytes (1.0 GB) copied, 0.821614 s, 1.2 GB/s
, 0.821645 s, 1.2 GB/s