CentOS - Dec 2008 - AHCI at boot?

I'm having trouble getting a Centos installation to boot on a system
with hdd's hanging off an AHCI hba.

Long ago, I posted about only seeing four of the six sata ports on my
asus server board.  According to research I've done since then (I now
need the ports!), the solution is to enable the AHCI bios, which turns
on NCQ and the last two ports.

The already installed system does not like the fact I've changed to
ahci and does not load the ahci module, eventually failing to boot
complaining it cannot mount the root fs, killing init, etc.

If I boot off the 5.2 installation dvd or a fedora 9 dvd, the kernel
boots just fine, loads up the ahci module and sees the drives no
problem.

So I'm wondering what config files I need to tweak, to help the
already installed system use the "new" ahci controller?  Previously,
it appears to have been using the piix module to access the drive with
the root fs on it.

I'm using the 64-bit 2.6.18-92.1.18 centosplus kernel (for XFS support).

The box is running an asus dsbf-de board, with 2x e5405 cpus and 16g
of ram.  There are six drives on the ahci, one 80g "system" drive (the
boot drive), and five 750g storage drives.  There is also a supermicro
8 port sata hba in the system, with five 250g drives on it.  The
supermicro uses the sata_mv module and is detected just fine.


Thanks for any suggestions!

Gordon

>So I'm wondering what config files I need to tweak, to help the
>already installed system use the "new" ahci controller? 
Previously,
>it appears to have been using the piix module to access the drive with
>the root fs on it.
So, you need modprobe.conf to reflect this as well as a new initrd.
On a similar system I have from Asus my modprobe.conf looks like this:

alias scsi_hostadapter ata_piix
alias scsi_hostadapter1 ahci

I assume the ata_piix is still required for the jmicron ide controller.
After editing this, run mkinitrd which will look there and then load the
required modules.

HTH,
jlc