hdparm / DMA problems

[Nyc0n]

To use hdparm to boost DMA speed, does DMA have to be enabled in the kernel?  i have the DMA enabled in the kernel, but some of my drives that should use it don’t, so I used hdparm to help that out, before hdparm I was getting 3megs a second after hdparm I was getting 30megs a second, I was like sweet! More than quadrupuled the speed, so I added the stuff to the hwtools file In my rcS.d directory (part of the hwtools package) and then rebooted…..i got the messages durning boot that DMA was being turned on etc, then I did the performance test again hdparm –Tt /dev/hd* and my speed when down to 8megs a second!!! What happened? Could the kernel be messing it up? Should I take out the kernel DMA stuff and just use hdparm?  I don’t understand why it would suddenly drop like that, I thought I was doing so well.  All these drives (I have 4) are 80gig or more WD 7200 rpm drives that I know support DMA and the like. So im not going to blow up my drives or send them to the moon as one tutorial put it, im just tring to get the full potential out of my drives.  I still doubled the throughput of the drives, but I would like to get that 30megs a second back. Can anyone help?   nick