UDMA Still Under Development

Support for IDE UDMA drives is largely complete, though some drives and chipsets are still under development. The Ultra-DMA Mini-HOWTO has the latest information on how and when to use UDMA.

It's worth noting that Windows has similar problems. A pair of articles in InfoWorld Magazine by Brian Livingston detail UDMA problems and solutions:

http://www.infoworld.com/cgi-bin/displayArchive.pl?/98/45/o02-45.38.htm

http://www.infoworld.com/cgi-bin/displayArchive.pl?/98/46/o02-46.46.htm