Problem:

I just activated the drive tweaks in Cpanel or attempted to perform manual harddrive tweaks using the hdparm program.
Now I see these errors in my system logs (/var/log/messages)
--SNIP--
Jan 9 23:28:18 18 kernel: hda: drive_cmd: status=0x51 { DriveReady SeekComplete Error }
Jan 9 23:28:18 18 kernel: hda: drive_cmd: error=0x04 { DriveStatusError }
Jan 9 23:28:18 18 kernel: ide: failed opcode was: 0xef
--SNIP--

Solution:

There are many different drive_cmd status and error codes, but these exact ones (status=0x51, error=0x04) are caused by trying to use hdparm to set a DMA mode that is not supported by the hard drive or ide interface hardware.

If this error has been produced by setting Cpanel hard drive tweaks, deactivate the hard drive tweak setting in Cpanel to prevent the errors from being produced on each reboot.

If this has been caused by manual use of hdparm, check the capabilities of the hardware by using the command '/sbin/hdparm -i /dev/DEVICE' and set a supported DMA mode. Review 'man hdparm' for information on how to use hdparm.

Most current linux OSes properly set the hard drive and IDE interface hardware for optimal performance by default and require no additional 'tweaks' or adjustments. Misuse of hdparm has been known to produce unexpected behavior and/or data loss.