Help Diagnose Slow Disc Access

[Alan Cox]

On Fri, 12 Feb 2010 10:59:22 -0600
Mikkel <mikkel at infinity-ltd.com> wrote:

> On 02/12/2010 05:40 AM, Alan Cox wrote:
> > 
> > You also want to avoid two disks on one cable as the IDE interface only
> > allows one of them to be active at a time so its a good way to cripple
> > performance.
> > 
> Dumb question - what happens if you have a slow interface on the
> CD/DVD drive? Does the driver change access modes depending on if it
> is talking to the master or slave, or does it pick the lowest common
> denominator? I seam to remember that being a problem at one time,
> but things have changed a lot sense then...

Most controller hardware supports switching the mode according to the
device. In some of the other cases the drivers (particularly the libata
ones) also know how to change mode in software when switching device.
SATA killed that problem off.

Modern hardware with AHCI interfaces enabled dump all the work on the
controller and allow multiple commands to be queued at once. That
improves things even further.

Alan