I have just successfully switched from IDE mode to ACHI mode on my mobo, but now all my HDD's show up in the safely remove hardware list. How do I stop this?
As administrator, open a command window and execute the following command to add registry keys for each of the SATA devices you want to hide:
reg.exe add "HKLM\SYSTEM\CurrentControlSet\Services\msahci\Controller(n)\Channel(m)" /f /v TreatAsInternalPort /t REG_DWORD /d 0x00000001
Change (n) for the controller number, e.g. 'Controller0'. Change (m) to the SATA port number e.g. Channel1, Channel2, Channel3... etc.
To get the controller and channel for your device, use Computer Management, then Disk Management and right click on the grey box entitled "Disk X" next to the disk graph display and then select Properties to bring up properties for the hardware device. Location is the controller, and channel is (not surprisingly) the channel.
Then reboot and the drives will no longer show.