ACHI support

[Alan Cox]

> It seems Windows users have more trouble than Linux users and it appears 
> if you are using RAID you can't use ACHI. It is implied that if you 
> don't use ACHI the speed of data transfer will be reduced in Serial Hard 
> Drives. So it is the old Lose-Lose situation where you never want to be.

Older Windows doesn't do AHCI without driver additions. Current Linux is
happiest with AHCI and will do raid and non-raid with AHCI generally
getting better performance too.

Alan