Re: [gentoo-user] OT: PATA performance

[Florian Philipp]

On Sat, 28 Jun 2008 23:19:26 +0200
Volker Armin Hemmann <volker.armin.hemmann@××××××××××××.de> wrote:

> On Samstag, 28. Juni 2008, Florian Philipp wrote:
> > Hi list!
> >
> > I've got a little question.  Here I've got a PC with two 40GB hard
> > disks, a CD-burner and a DVD-burner, all PATA. Now I'm running out
> > of disk space and I'm thinking about ways to increase it:
> >
> > 1. I could replace the older 40GB disk with a new model but I'd
> > hate to trash it because it's working alright.
> >
> > 2. I could replace the really old and rather useless CD-burner with
> > a disk. However, that would mean I'd have to attach the DVD-burner
> > and one of the disks to the same controller. Now I'm asking myself
> > (and you ;) ) how that would affect performance.
>
> wikipedia can answer that.

"'One operation at a time'

This is caused by the omission of both overlapped and queued feature
sets from most parallel ATA products. Only one device on a cable can
perform a read or write operation at one time, therefore a fast device
on the same cable as a slow device under heavy use will find it has to
wait for the slow device to complete its task first.

However, most modern devices will report write operations as complete
once the data is stored in its onboard cache memory, before the data is
written to the (slow) magnetic storage. This allows commands to be sent
to the other device on the cable, reducing the impact of the "one
operation at a time" limit.

The impact of this on a system's performance depends on the
application. For example, when copying data from an optical drive to a
hard drive (such as during software installation), this effect probably
doesn't matter: Such jobs are necessarily limited by the speed of the
optical drive no matter where it is. But if the hard drive in question
is also expected to provide good throughput for other tasks at the same
time, it probably should not be on the same cable as the optical drive."

So I can hope that caching will negate any negative effects as long as
one of the drives is much faster than the other (e.g. optical and hard
disk drive) even when I'm streaming a (theoretically) constant byte
stream from one to the other (ripping, burning)?

>
> But why not a cheap sata controler and a nice big sata disk? They are
> cheaper now than PATA disks.

cheap SATA-controller:	EUR 35
cheap 160GB SATA-disk:	EUR 35
cheap 160GB PATA-disk:	EUR 40
cheap 250GB PATA-disk:	EUR 45

Not cheap enough it seems ;)
It would be more price efficient to trash one of the current disks for
the new one than buying a new controller.

By the way: Actually the mobo has two SATA-controllers but one of them
crashes on POST while the other one doubles the time the POST takes.
That's why they are both deactivated.