SATA disks as AHCI

[Paavo]

Hi,

I have a Fedora 9 system, which works fine.

It has Asus P5Q motherboard Intel P35 chipset, i.e. ICH10), which has an option in BIOS how to use SATA disks, the default is IDE, and the other options are AHCI and RAID.

I don't need RAID, but AHCI would be nice because of native command queueing and perhaps also hot-plug.

When I change the BIOS setting from IDE to ACHI, the system does not fully boot, I think it cannot mount root filesystem. Boot stops somewhere udev should load. But the first phases of the boot work just fine, so what is the problem why this does not boot up properly?

There are two physical disks, sda1 is / (ext3), sda2 is swap, sdb1 is /something (ext3) and sdb2 is swap. Both are Seagate 7200.11 500GB SATA devices.

/etc/fstab has UUID for all 4 partitions, I haven't tried /dev/sd?? definitions yet.

What should I do to enable using the SATA BIOS setting? Do I need some kernel parameter for libata or something?

-Paavo

[Firewing1]

It's possible to switch to/from AHCI after installing Fedora, but it gets a bit complicated because you'll need to use the rescue CD to generate a new ramdisk which includes the AHCI kernel modules. I've played around with the same option on my Gigabyte board and I didn't find much improvement with AHCI - I would just leave it on IDE mode. As for hotplugging, unless I'm mistaken Fedora supports that in IDE or AHCI mode. I'm not sure if it's real hotplug it just the way the kernel's been designed, but I can plug/unplug my eSATA drives as many times as I want and they'll mount like normal each time.
Firewing1

[Paavo]

So stock initrd's don't have AHCI support? Or are those built in every machine when installing new kernel containing just what's needed?

# ls -axl /boot/config-2.6.26.5-45.fc9.i686
-rw-r--r-- 1 root root 88852 2008-09-20 10:54 /boot/config-2.6.26.5-45.fc9.i686

# grep -i ahci /boot/config-2.6.26.5-45.fc9.i686
CONFIG_SATA_AHCI=m

So this is not enough? Should it be CONFIG_SATA_AHCI=y to make boot fully work?

If new kernel/initrd is needed, what is the easiest way to do it?

[Firewing1]

Yup, if you compile with built-in support then you're safe, but mkinitrd will only take the modules that are needed to boot the running kernel - meaning that unless you can boot the machine into Fedora with AHCI on and then run mkinitrd, it won't take it by default.

You can use the --preload option to manually specific modules though, so you could always try turning AHCI off, booting Fedora, making your custom image:

mkinitrd --allow-missing --preload=ahci --force-scsi-probe /boot/initrd-`uname -r`-custom `uname -r`

Then reboot, enable AHCI and during the GRUB bootup menu edit the "initrd" line to load the custom image you just created. When that's done, reinstall the latest kernel (or yum update one) to create a good initrd.
Firewing1