dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync
hdparm -tT /dev/sda

[root@sv14uk ~]# dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync
16384+0 records in
16384+0 records out
1073741824 bytes (1.1 GB) copied, 3.64116 s, 295 MB/s

[root@sv14uk ~]# hdparm -tT /dev/sdb

/dev/sdb:
Timing cached reads: 14754 MB in 2.00 seconds = 7387.35 MB/sec
Timing buffered disk reads: 770 MB in 3.00 seconds = 256.61 MB/sec

[root@sv16uk ~]# dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync
16384+0 records in
16384+0 records out
1073741824 bytes (1.1 GB) copied, 7.83822 s, 137 MB/s

[root@sv16uk ~]# hdparm -tT /dev/sda

/dev/sda:
Timing cached reads: 25272 MB in 2.00 seconds = 12657.18 MB/sec
Timing buffered disk reads: 352 MB in 3.01 seconds = 117.13 MB/sec