$ hdparm -Tt /dev/sdb
/dev/sdb:
 Timing cached reads:   3358 MB in  2.00 seconds = 1679.46 MB/sec
 Timing buffered disk reads:  452 MB in  3.01 seconds = 150.05 MB/sec

$ hdparm -Tt /dev/sdb
/dev/sdb:
 Timing cached reads:   3372 MB in  2.00 seconds = 1685.85 MB/sec
 Timing buffered disk reads:  274 MB in  3.00 seconds =  91.23 MB/sec

$ hdparm -Tt /dev/sdb
/dev/sdb:
 Timing cached reads:   3360 MB in  2.00 seconds = 1680.70 MB/sec
 Timing buffered disk reads:  324 MB in  3.01 seconds = 107.63 MB/sec

$ hdparm -Tt /dev/sdb
/dev/sdb:
 Timing cached reads:   3304 MB in  2.00 seconds = 1652.26 MB/sec
 Timing buffered disk reads:  252 MB in  3.01 seconds =  83.62 MB/sec