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ide dma doesn't work

I'm running a vanilla sarge install on a 2.8GHz P4, booting from a SCSI
disk. There's a SATA disk and an IDE. The IDE disk is hda. The
motherboard is an Intel 865.

When writing a big file to hda, the CPU usage goes to 100% and stays
there for a long time. And it takes a lot longer to write to hda than to
the others. I interpret that to mean the system is doing programmed I/O
instead of DMA.

hdparm -i /dev/hda says udma5 (out of a possible 6) is the transfer

hdparm /dev/hda says 
"using_dma = 0 (off)" 

hdparm -d1 /dev/hda says  
"setting using_dma to 1 (on)
 HDIO_SET_DMA failed: Operation not permitted"

I've looked at the kernel config and the modules and lsmod. As best I
can tell all the IDE code is there -- that definitely doesn't mean it
is. I've tried this with a Quantum 20G and a Maxtor 200G with exactly
the same results (except the older drive does udma2, max). 

I googled and went through the tutorial at 


but got nothing like the I/O speed improvements shown there. I got only
a 5 or 10 percent improvement.

What am I not understanding? 

Glenn English

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