On Thu, Jan 20, 2005 at 10:22:12AM +0200, Mihai CHELARU wrote:
> Manuel Bouyer wrote:
> >Note that, with this hardware configuration, you can't even paralelize
> >accesses to the hardware, because you have 2 disks per IDE channel (so
> >some access have to be serialized). Things would be a bit better if you 
> >could
> >have one disk per channel (for each write, you have to write data and
> >partity, at last if those can be paralelized, you get soome performance
> >boost).
> 
> True, but even in this case I should expect the performance to be near 
> the performance one hard disk has, isn't it ?

At best it will be 1/2 the performance of one hard disk (for one write,
you have to do one read and 2 writes). With your setup (2 disk per IDE
controller) it's likely to be more like 1/3. Then, because you have
one read followed by one write for the same block, you don't have a sequential
I/O on the disk, so things gets even worse, possibly by a large amount
(performances drop significantly when you start doing seeks).

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la difference
--