Friday, March 2, 2012

Enabling AHCI/RAID on Windows 8 after installation

UPDATE: MS has recently published a KB article on a simpler way to address this. Thanks to commenter Keymapper for the heads up!

Been playing around with Windows 8 Consumer Preview and Windows 8 Server recently. After installing, I needed to enable RAID mode (Intel ICH9R) on one of the machines that was incorrectly configured for legacy IDE mode (why is this the default BIOS setting Dell?). In Win7, you would just ensure that the Start value for the Intel AHCI/RAID driver is set to 0 in the registry, then flip the switch in the BIOS, and all's well. Under Win8 though, you still end up with the dreaded INACCESSIBLE_BOOT_DEVICE. The answer is simple enough: turns out they've added a new registry key underneath the driver you'll need to tweak: StartOverride. I just deleted the entire key, but if you're paranoid, you can probably just set the named value 0 to "0".

So, the full process:

- Enable the driver you need before changing the RAID mode setting in the BIOS:
(for Intel stuff, the driver name is usually iaStorV or iaStorSV, others may use storahci)
-- Delete the entire StartOverride key (or tweak the value) under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\(DriverNameHere)
- Reboot to BIOS setup
- Enable AHCI or RAID mode
- Profit!