DMA for a Plextor CDRW?

[david at thekramers.net (David Kramer)]

I just got a Plextor PX-W2410TA 24/10/40A burner*.  The documentation says
that it's best to use it in DMA mode.

Some initial poking around leads me to believe that I can use hdparm to 
change that.  Is it really that easy though?  Is there any disadvantage?  
What's the worst that can happen if I try it?  Do I need to put the call 
to hdparm in /etc/rc.local, or is there some standard config file to put 
it in?

While I'm at it, I assume it does no good if your hard drive is also 
configured for DMA, right? 

My motherboard is a Spacewalker HOT-569A, and the manual says it can do 
UDMA 33, so I assume that won't be a problem.  The hard drive is a WDC 
400EB, which looks like it supports DMA also, so maybe I should turn it on 
for that too.

BTW, this is Red Hat 7.0 with all upgrades, including kernel 2.2.19-7.0.15.


* Before y'all get jealous, I'm replacing my ancient "Early Adopter 
Special" Philips OmniWriter, with 2X write.  They advertised it with a 2MB 
buffer but it really only has 1MB.  SCSI I centronics interface.

----------------------------------------------------------------------------
DDDD   David Kramer         david at thekramers.net       http://thekramers.net
DK KD  Some people have told me they don't think a fat penguin really 
DKK D  embodies the grace of Linux, which just tells me they have never seen 
DK KD  an angry penguin charging at them in excess of 100mph. They'd be a 
DDDD   lot more careful about what they say if they had.      Linus Torvalds