I have RAID1 (mirror) with two drives, using ICH10R fake-raid on my motherboard. I hope that if I break the mirror using the RAID BIOS, all data on both drives will still be intact. I'd love to have a confirmation from someone who already did this.
In my experience, you can set it to AHCI and still boot off of one drive, while losing the redundancy. However, if you are using this RAID partition as your main OS, you could experience some driver issues (or BSOD on Windows).
EDIT: If you receive BSOD Message STOP 0x0000007B INACCESSABLE_BOOT_DEVICE
Consider the following scenario. In the BIOS setup of a Microsoft Windows 7 or Windows Vista-based computer, you change the Serial Advanced Technology Attachment (SATA) mode of the boot drive to use the either Advanced Host Controller Interface (AHCI) specification or RAID features. You then restart the computer. In this scenario, you receive the following error message: STOP 0x0000007B INACCESSABLE_BOOT_DEVICE
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: 322756 How to back up and restore the registry in Windows To resolve this issue yourself, enable the AHCI driver in the registry before you change the SATA mode of the boot drive. To do this, follow these steps: