Comment 12 for bug 910999

This bug also coincides with the "Used" count given by lsmod against the ahci kernel module being either 5 or 6, instead of 2 when it works on older kernels.

I have also tried forcing the ahci module to be loaded before others (by placing 'ahci' in /etc/initramfs-tools/modules, running 'sudo update-initramfs -u' and rebooting). It makes no difference.