Okay, I've got an ASUS motherboard with RAID, 2 40 gig hard drives on RAID. On the primary IDE channel I have my Pioneer DVD-ROM drive set to master, on secondary IDE I have my Plextor 40/12/40 CD-RW drive. I know both of these drives work perfectly in DMA mode, but for some reason I can't enable it.
I built the computer myself, and when I was fiddling with it initially I noticed that playback of video files off a disc in my DVD drive would stutter, but not if I played the same disc in my CD-RW drive. Turned out that the DVD drive was running in PIO mode, even though it should have been in DMA, and the CD drive was running in DMA. I never got around to trying to fix this, because I kinda sorta accidentally reinstalled windows shortly after I noticed this, and, what do you know, afterwards, both drives ran in DMA and have worked perfectly since.
Except that sometime in the past week or so, they BOTH decided to turn DMA off. I don't have any idea what might have caused this, I haven't been fiddling with drivers for quite a while, and nothing else is giving me trouble. I've checked the BIOS, DMA is enabled for both drives there, and I have "Use DMA if available" set in Windows Device Manager, but it still shows them both as running in PIO mode. Any help or ideas on how to correct this would be greatly appreciated!
Ive seen similar issues on a variety of systems. Getting DMA to 'stick' seems to be very much a random process.
The technical reason for UDMA not sticking is that windows THINGS that data integrity has been somehow compormised, so it kicks the drive back to PIO.
Things that can be done to get DMA enabled:
Delete and reinstall Optical drives in device profile then reboot.
Reinstall Latest Chipset drivers.
Delete then reinstal Primary and/or secondary IDE controller in device profile then reboot.
Replace IDE cables that my or maynot be faulty.
Sacrifice a chicken to the deity of your choice.
I had the same thing on my asus board. the solution was to uninstall intel application accelerator. this uninstalled the ide channels, and when windows reinstalled them on reboot, I was able to set DMA and it stuck. (Just uninstalling the IDE channels myself, without uninstalling intel application accelerator did not solve the problem)
I tried uninstalling the drives and IDE channels, and when Windows reinstalled them on reboot, lo and behold, they were working fine again! Still seems a little screwy that something like that could just change itself all of the sudden, but I guess that's Windows for you. Thanks to everyone for their suggestions, I really appreciate the help!