Question regarding heavy CPU during disk i/o

[J Marler <jmarler-du@emarler.com>]

I am running Debian Woody on a K7 850Mhz system with 384MB of RAM.

My motherboard is an Abit KT7-RAID with VIA chipset and VIA IDE
controllers.  I have a Western Digital 60GB WDC600BB UDMA 100 hard
drive, currently running only UDMA 66.  I have the RAID controller
disabled for simplicity sake (that may be a mistake as only the RAID
controller will do UDMA 100).

My question is this:  Whenever I do any kind of "heavy" disk access,
such as copying large files (10MB+), the CPU usage sky rockets and my
system reacts slowly.  Why?  And how do I fix this?

I have DMA access disabled with hdparm.  If I enable it, the system
promptly locks hard.  I have multicount enabled at 16.  32-bit i/o is
enabled.  readahead is enabled at 8.  busstate is 1 (not sure what that
is.)

I am sure there is a simple answer to my question, but I have tinkered
with this thing for too long now.  I can't seem to figure it out.

Any help would be greatly appreciated.

Please copy me at jmarler-du@lists.debian.org on any replies as I am not
subscribed to this list.

Thank you.

Jon