RE: install sloooow doooown

According to my knowledge [which may be wrong, engineers know better than
I],
	1) The only penalty for mixing CDROms and harddrives on the same IDE chain
is if the CDROM
	is a PIO device. This causes the controller to have to switch modes or lock
down into either UDMA
	or PIO mode. There are some versions of the Intel disk controller chip that
act in a weird way
	and can not tolerate mixed mode devices oin either chains. i ran into this
on a ASUS motherboard.
	Later model cdroms (*12x and above should have UDMA/33 mode or
	better. Advice only use UDMA capable cdrom/dvd drives, toss out the older
cdrom drives under 24X

	2) ideally both devices should be of same type interface and speed
UDMA/33, UDMA/100, etc.,
	and the controller should have greater than or equal interface capabilities
to the drives.

	3) There should be NO speed penalty if the two drives on a single chain are
different speeds -
	the controller only selects
	and latches data from one drive at a time and at that drives rated speed.
Only the EIDE interface
	on the selected drive should be involved in clocking the data.

	4) Mixing hard drives and CDROMs on same IDE chain impacts the performance
of the hard drive
	only when the CDROM is active at the same time as the harddrive. that is
because the CDROM takes alot
	longer to READ data than the hard disk, it being a slower device. If you
are not using the cdrom drive
	then it will not be selected and wont interfere on the IDE bus. The hard
drive should run at the
	fastest speed of the controller or the hard drive, whichever is the
slowest.

	5) The controller should probe the disk drive interface on boot and
determine it's capabilities
	and adjust performance settings on a per drive basis.

	I have a server here with 3 UDMA/66 disk drives and  a UDMA 33 cdrom drive.
The master hard drive
on each io chain is mirrored to the other. I guarantee that the two mirrored
drives are running at the same speed
despite the slower cdrom slave drive on the second ide chain. You could
always scan Intel.com, etc. to see what their IDE controller chip engineers
have recommended.

++> -----Original Message-----
++> From: [email protected]
++> [mailto:[email protected]]On Behalf Of Ernie Schroder
++> Sent: Tuesday, March 04, 2003 7:10 PM
++> To: [email protected]
++> Subject: Re: install sloooow doooown
++>
++>
++> On Tuesday 04 March 2003 15:12,
++> [email protected] wrote:
++> >You should never install IDE drives on the same
++> > channel.
++>
++> Would someone tell me why this is right? I've always worked
++> under the
++> assumption that 2 devices on the same IDE channel would
++> both operate at
++> the speed of the slower drive, thus if I had an UDMA 100
++> hard drive and
++> a CD-ROM on the same channel, they would both run at UDMA
++> 33, whereas
++> if I had 2 UDMA hard drives on the same channel, they would
++> operate at
++> their full speed, assuming my controller could handle that. I have
++> always read that mixing hdd's and cd-roms on the same
++> channel was poor
++> practice.
++> 	Who's right? I do see something to be said for Stew's
++> way of thinking,
++> though it's not that often that your 2 hdd's write to each
++> other and
++> even when that happens, it seems to me that data can move between 2
++> UDMA100 drives faster than between a UDMA 33 drive and a UDMA 100.
++>
++> --
++> Regards, Ernie
++> 100% Microsoft and Intel free
++>
++>
++>
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++>