windows 7 - BIOS setting: AHCI or RAID (when using SSD + 2x hard drive in RAID-0)

  • nixda

    I want to add a new SSD and use it as system drive with Windows 7 x64 installed.
    As driver I chose newest Intel Rapid Storage driver (not MSAHCI). I know that I have to use AHCI as BIOS setting for optimal SSD read/write performance. But I'm also using 2 normal hard drives as separate RAID-0

    SSD: Windows 7
    hard drive: RAID-0
    hard drive: RAID-0

    If I set my BIOS on my Asus P5W DH Deluxe to AHCI, my RAID-0 cant be recognized
    And If I'm using RAID as setting, maybe my SSD has not its top speed. But I'm not sure about that.

    In short:
    AHCI > no RAID-0
    RAID > no optimal SSD performance (?)

    Now my question: Can I use RAID as BIOS setting and be sure, that theres no decrease in SSD performance?

    Google finds so many articles with similar topics and my head is just exploding. Two examples:
    - set AHCI and after installing OS switch to RAID as BIOS setting... what?
    - use a diskette and F6 while installing Windows 7... really? O.o I thought those times are gone

  • Answers
  • Shinrai

    RAID should support everything AHCI does for an SSD that isn't actually in an array; no reason for concern.

    (On a tangential note, I've benchmarked better speeds using the msahci driver than the Intel one even on Intel drives. If you're that concerned you might check it out.)

  • ThePCpenguin

    There is one important thing to be noted here:

    As soon as your RAID is built, it is identified by the OS as a single whole and you cannot access its constituents separately. This may be inconvenient. For example, you won't be able to update the firmware or view the S.M.A.R.T. information or perform a Secure Erase for the SSDs in your RAID. But the biggest problem is that the OS won't be able to use the TRIM command which is supposed to protect SSDs from performance degradation.

    To sum up, SATA RAID controllers, including those in modern chipsets, do not support the TRIM command. As a result, the array’s writing performance degrades over time whereas single SSDs are less susceptible to this problem.

  • Related Question

    Windows 7 New SSD SATA AHCI?
  • aherrick

    I recently got a new laptop (Dell Latitude E6410) which came with a regular hard drive. I removed the hard drive and installed Windows 7 64 bit fresh. I've been doing some reading about possibly changing a BIOS setting under SATA Operations. Currently it is set to "RAID On" but AHCI is also an option. Apparently I need to tweak the registry the reboot and flip to AHCI in order enable it.

    My question is what exactly is it and why would I want to enable it? Will it provide faster performance with my SSD? Is this even necessary to switch to AHCI or should I leave the BIOS alone and stay with RAID On.

  • Related Answers
  • Paul

    raid off, ahci on with a new ssd installed. Raid uses 2 drives and "splits" files and uses the 2 drives to work together for faster/better perfomance. Or raid can use 2 drives and one is a exact copy of the other as you go. I installed a ssd in my dell laptop and it is screaming fast! Way faster then the hdd that was in there. You must enable ahci in the bios for running most ssd drives. If you buy one, it will tell you to do that in the limited paperwork that comes with it. Best upgrade for the speed i have ever done.

  • Jeff Atwood

    Per this performance comparison, it doesn't seem to be urgent for a single user workstation. AHCI is a better more modern option and you should always use it when you can, though.

    From that article:

    • If your application requires hot-plug drive support or redundant disks, then AHCI is the only choice.

    • IDE mode can occasionally benefit from slightly faster read and write speeds in some tests.

    • TRIM support works in both modes fine

    • Overall, most SSD drives deliver better performance in AHCI mode, but it is not night and day.

    How do you know you're using IDE or AHCI? Go to Device Manager and expand the hard drive controllers. If you see "AHCI" in there, you are using AHCI.

    device manager, IDE ATA/ATAPI controllers

    The good news is that you can switch from IDE mode to AHCI in Windows 7 or Vista without reinstalling or even opening your PC case.

    1. Start Regedit
    2. Open HKEY_LOCAL_MACHINE / SYSTEM / CurrentControlset / Services
    3. Open msahci
    4. In the right field left click on "start" and go to Modify
    5. In the value Data field enter "0" and click "ok"
    6. Close Regedit
    7. Reboot and enter BIOS (hold Delete key while Booting)
    8. In your BIOS select "Integrated Peripherals" and OnChip PATA/SATA Devices. Now change SATA Mode from IDE to AHCI.
  • Dr. Gianluigi Zane Zanettini

    Note that Intel recommends RAID for SATA drives, even with a non-RAID storage setup:

    If you are using a SATA hard drive, set your BIOS to RAID mode. RAID mode provides the greatest overall flexibility and upgradeability because it allows your system to be RAID ready and enable AHCI.