Change RAID to AHCI in Windows 7

https://answers.microsoft.com/en-us/windows/forum/windows_7-hardware/changing-from-raid-to-ahci/4c94f678-6bd1-48a6-b871-8872c841023a
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OB

O. Bilal [MSFT]

Hi Thomas,
Thank you for your post.
I believe I have the solution to your problem and I verified it against a Dell machine that has similar controller with your machine. Changing from AHCI to RAID,http://support.microsoft.com/kb/922976 fix will work.
Changing from RAID to AHCI, you need one more step. Msahci driver requires Atapi.sys miniport to be loaded during boot as well. So you need to change theStart value to 0 for both of the following entries in your registry. You can use regedit.exe utility.
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\msahci
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\atapi
Or you can also simply run the below command lines in an elevated window.
REG ADD HKLM\System\CurrentControlSet\Services\msahci /v Start /d 0 /f /t REG_DWORD
REG ADD HKLM\System\CurrentControlSet\Services\atapi /v Start /d 0 /f /t REG_DWORD

Regards

 }

 I tried the above and worked. Just these two values.

For more detailed instruction, follow the given link  http://support.microsoft.com/kb/922976

 To resolve this issue, enable the AHCI driver in the registry before you change the SATA mode of the boot drive. To do this, follow these steps, but no need to do the IastorV: 

1. Exit all Windows-based programs.
2. Click Start, type regedit in the Start Search box, and then press ENTER.
3. If you receive the User Account Control dialog box, click Continue.
4. Locate and then click one of the following registry subkeys:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\IastorV
5. In the pane on the right side, right-click Start in the Name column, and then click Modify.
6. In the Value data box, type 0, and then click OK.
7. On the File menu, click Exit to close Registry Editor.

You must change the boot mode using your BIOS setup.
In Dell E6420, press KEY F12.

I noticed that AHCI is faster in writing than RAID using USERBENCHMARK.


AHCI with Intel drivers:

Read 397 Write 360 Mixed 320 SusWrite 136 68% 304 MB/s

4K Read 21.8 4K Write 29.1 4K Mixed 23.5 79% 24.8 MB/s

DQ Read 281 DQ Write 236 DQ Mixed 25.7 83% 181 MB/s

 AHCI with Microsoft drivers:

Read 284 Write 367 Mixed 314 SusWrite 130 62% 274 MB/s

4K Read 20.7 4K Write 58.3 4K Mixed 27.5 98% 35.5 MB/s

DQ Read 255 DQ Write 198 DQ Mixed 39.6 80% 164 MB/s

 RAID:

Read 377 Write 341 Mixed 292 SusWrite 141 64% 288 MB/s

4K Read 20.4 4K Write 28.8 4K Mixed 22.3 75% 23.8 MB/s

DQ Read 286 DQ Write 245 DQ Mixed 164 151% 232 MB/s