When I run hdparm -tT /dev/sda command under CentOS / RHEL I get the following error on screen:

/dev/sda:
Timing buffered disk reads: 908 MB in 3.00 seconds = 302.39 MB/sec
HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for device

How do I fix this problem?

hdparm provides a command line interface to various kernel interfaces supported by the Linux SATA/PATA/SAS “libata” subsystem and the older IDE driver subsystem. Some options may work correctly only with the latest kernels. So first make sure you’ve latest kernel update installed:

# yum -y update
To fix this error message, you need to install latest version of hdparm. RHEL CentOS / Linux comes with an older version. To download latest version visit this webpage. You can also use wget as follows:
# wget http://downloads.sourceforge.net/project/hdparm/hdparm/hdparm-9.9.tar.gz
Untar hdparm-9.9.tar.gz:
# tar -zxvf hdparm-9.9.tar.gz
Compile hdparm:
# cd hdparm-9.9
# make
Run latest hdparm from the current directory:
# ./hdparm -tT /dev/sda
Sample Outputs:

/dev/sda:
 Timing cached reads:   4686 MB in  2.00 seconds = 2346.22 MB/sec
 Timing buffered disk reads:  888 MB in  3.00 seconds = 295.55 MB/sec