[root@super PHP]# blockdev --getra /dev/sdc1
256

[root@super PHP]# hdparm -tT /dev/sdc1

/dev/sdc1:
 Timing cached reads:   4464 MB in  2.00 seconds = 2231.22 MB/sec
 Timing buffered disk reads:  436 MB in  3.01 seconds = 144.68 MB/sec
[root@super PHP]# hdparm -tT /dev/sdc1

/dev/sdc1:
 Timing cached reads:   4576 MB in  2.00 seconds = 2288.35 MB/sec
 Timing buffered disk reads:  432 MB in  3.00 seconds = 143.78 MB/sec
[root@super PHP]# hdparm -tT /dev/sdc1

/dev/sdc1:
 Timing cached reads:   4504 MB in  2.00 seconds = 2250.09 MB/sec
 Timing buffered disk reads:  436 MB in  3.01 seconds = 144.68 MB/sec

[root@super PHP]# blockdev --setra 512 /dev/sdc1


[root@super PHP]# hdparm -tT /dev/sdc1

/dev/sdc1:
 Timing cached reads:   4456 MB in  2.00 seconds = 2227.22 MB/sec
 Timing buffered disk reads:  436 MB in  3.01 seconds = 144.97 MB/sec
[root@super PHP]# hdparm -tT /dev/sdc1

/dev/sdc1:
 Timing cached reads:   4488 MB in  2.00 seconds = 2244.34 MB/sec
 Timing buffered disk reads:  436 MB in  3.00 seconds = 145.11 MB/sec
[root@super PHP]# hdparm -tT /dev/sdc1

/dev/sdc1:
 Timing cached reads:   4540 MB in  2.00 seconds = 2268.08 MB/sec
 Timing buffered disk reads:  436 MB in  3.00 seconds = 145.11 MB/sec