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I have two servers running RHEL 5.4 quite happily. However, through simple oversight, AHCI/hotswap support was not enabled in BIOS at install time and is now needed. The machines are running ICH10R SATA controllers and kernel-xen-2.6.18-164.el5.

I tried restarting with AHCI enabled, but quite predictably, the machine refused to boot. There doesn't seem to be much online in the way of instructions for doing this in Linux, although there is a plethora of information on enabling AHCI post-install on Windows. I take it grub is the component choking, presumably because the change in driver messes with its device mappings?

What is the best way to go about enabling AHCI on an already running Linux installation?

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up vote 2 down vote accepted

Where does the boot fail? After loading grub - does the kernel panic saying it can't find root?

Going from IDE to AHCI will mean you need to change the driver from the IDE driver to the AHCI one (called 'ahci')

You'll probably need to update /etc/fstab to /dev/sdX, and add a line like "scsi-hostadapter1 ahci" to /etc/modprobe.conf, and then rebuild your initrd (e.g. mkinitrd -f -v /boot/initrd-$(uname -r).ahci.img $(uname -r))

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I rebuilt the ramdisk using mkinitrd --allow-missing --preload=ahci --force-scsi-probe /boot/initrd-`uname -r`-custom `uname -r` following instructions at – JeffG Mar 9 '11 at 21:15

I know nothing about AHCI, but searched anyways. First off, are you certain AHCI has been implemented in the RedHat kernel?

This Wiki link HERE indicates that it is added by default as of 2.6.19, but you're running 2.6.18.rhel.

I'd ask HERE if anyone can tell you if RHEL5.4 supports this...

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RHEL5.4 definitely supports ahci. – James Sep 29 '09 at 22:23

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