From Bugzilla Helper: User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.1) Gecko/20020830 Description of problem: DMA cannot be set to "on" (with hdparm) on DVD players. DMA capable CD-ROMs may also be affected. Version-Release number of selected component (if applicable): How reproducible: Always Steps to Reproduce: 1. assuming /dev/hdc as the DVD unit 2. hdparm -d1 /dev/hdc Actual Results: ~# hdparm -d1 /dev/hdc /dev/hdc: setting using_dma to 1 (on) HDIO_SET_DMA failed: Operation not permitted using_dma = 0 (off) Expected Results: ~# hdparm -d1 /dev/hdc /dev/hdc: setting using_dma to 1 (on) using_dma = 1 (on) Additional info: It used to work under RedHat 7.3 Workaround: upgrade the kernel to 2.4.19 Notes: DMA off leads to jerky playback and system responsivness
From the release notes: o DMA is disabled on CD-ROM drives in this release in a different but more reliable way than previously. If you are sure that your CD-ROM drive is capable of IDE DMA, place the following line in the /etc/modules.conf file: options ide-cd dma=1