pbharris is correct . Here is a smippet of my /etc/sysconfig/harddisk file :
AS you can see, I just uncommented the lines. I seem to have fine DMA with my DVD, so I suppose that is the only spot to make it to work right.
# These options are used to tune the hard drives -
# read the hdparm man page for more information
# Set this to 1 to enable DMA. This might cause some
# data corruption on certain chipset / hard drive
# combinations. This is used with the "-d" option
# Multiple sector I/O. a feature of most modern IDE hard drives,
# permitting the transfer of multiple sectors per I/O interrupt,
# rather than the usual one sector per interrupt. When this feature
# is enabled, it typically reduces operating system overhead for disk
# I/O by 30-50%. On many systems, it also provides increased data
# throughput of anywhere from 5% to 50%. Some drives, however (most
# notably the WD Caviar series), seem to run slower with multiple mode
# enabled. Under rare circumstances, such failures can result in
# massive filesystem corruption. USE WITH CAUTION AND BACKUP.
# This is the sector count for multiple sector I/O - the "-m" option
# (E)IDE 32-bit I/O support (to interface card)
# Enable drive read-lookahead
# Add extra parameters here if wanted
# On reasonably new hardware, you may want to try -X66, -X67 or -X68
# Other flags you might want to experiment with are -u1, -a and -m
# See the hdparm manpage (man hdparm) for details and more options.