SIS 5513/IBM Deskstar HDIO_SET_DMA Operation not permitted?

2.2 allowed me to set DMA on an SIS 5513 using an IBM Deskstar 40 gig IDE. 2.4 goes "Operation not permitted" when I try it.

Why?

I hit it with ide0=ata66 in lilo, and it sped up from 3 megs/sec to 5 megs/second, but I used to get 12. hdparm /dev/hda still says I'm not using DMA.

I realise I'm doing dangerous stuff here to get the performance back. I'm just curious why it's not doing it for me. (Is there a known problem I should be worried about?)

Let's see, ide0=dma,ata66... right? Should I be really really worried about my data integrity if I do this? It never had a problem under 2.2...

Rob

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