hdparm /dev/hda

...or...

hdparm -I /dev/hda

...for really detailed info, or....

hdparm -i /dev/hda

...for some terse info.

Note you do NOT specify the partition number as we're just looking at the drive.

Among other things, you'll see an entry that says 'using_dma', indicating whether this drive has DMA on or off. (CAVEAT: messing with hdparm is not something you would do on a live, production system! Although I have never experienced it, messing with the settings could corrupt your disk!)

To turn DMA off, type...

hdparm -d0 /dev/hda

...or to turn it back on...

hdparm -d1 /dev/hda

OK, maybe you think I'm making this up - how do I tell if it really turned on or off? Well, turns out hdparm can run a benchmark test for you. To do so, type...

hdparm -tT /dev/hda

You will get a report after a bit. At least on my system here I saw an improvement of 9X on my buffered disk reads.

hdparm -c3 -d1 -a16 -p4 -X udma2 -M128 /dev/hda

With these results:

 Timing buffer-cache reads:   128 MB in  0.83 seconds =154.22 MB/sec
 Timing buffered disk reads:  64 MB in  2.58 seconds = 25.10 MB/sec

...with the caveat that UDMA2 is the fastest mode it will take. The -M128 puts it in accoustically quiet mode, but I can't tell a difference.

Lastly, you can read this nice article for more info, esp on getting DMA to turn on for fussy motherboards.

http://linux.oreillynet.com/pub/a/linux/2000/06/29/hdparm.html

-- MattWalsh - 22 Oct 2002