Controller: SATA, RAID, and AHCI

Discussion in 'Memory and Storage' started by Satsuki, Jun 16, 2009.

  1. Satsuki

    Satsuki Member

    Joined:
    Jan 5, 2009
    Messages:
    29
    Likes Received:
    0
    Hey everyone!

    Can someone elaberate on this quote?

    "Intel recommends choosing RAID mode on their motherboards (which also enables AHCI) rather than the plain AHCI/SATA mode for maximum flexibility, due to the issues caused when the mode is switched once an operating system has already been installed."

    I first installed Windows XP on a 250GB HD in SATA mode. I then installed Windows 7 on two 500GB HDs (RAID 0) in RAID mode.

    I can't detect my 250GB in 7, but I can in the BIOS. Is this due to switching modes? Do SATA/RAID controllers only support one configuration at a time?

    Could someone give me general non-super-technical information about AHCI? I hear it allows SATA to use NCQ and hot-plugging. Anything else?

    I have a AHCI mode, what's the difference between RAID and AHCI modes? I know enabling RAID will automatically enable AHCI.

    Any other information/tips to configuring different modes would be great! :)

    Thanks a billion,
    Satsuki

    I had to do some major spring cleaning in this thread due most of the posts being wildly off topic

    Keep it relevent; take the rest to the Off Topic forum.

    n7
    Memory/Storage Mod
     
  2. Loading...


  3. MerlinRML

    MerlinRML Senior member

    Joined:
    Sep 9, 2005
    Messages:
    207
    Likes Received:
    0
    This is very misleading. XP has no included drivers for AHCI, sure, but it is a fairly straightforward process to add them. Granted, it's getting harder due to lack of floppy drives in a lot of systems...


    AHCI is a protocol, like a language. The AHCI SATA mode and the AHCI RAID mode of your motherboard are two different modes that each speak the same language. Sure they speak the same language, but that doesn't mean if you use AHCI RAID mode that it works exactly the same as AHCI SATA mode. For the sake of understanding, I think it's easier to think of AHCI mode and RAID mode as mutually exclusive, even though they share a common protocol.

    When in AHCI mode, you need an AHCI driver (not included by default in XP, but included in Vista). You do have additional capabilities over IDE (sometimes called Legacy) mode like hot-swap support and NCQ. The controller allows direct access to any device it can see.

    When in RAID mode, you need the Intel Matrix RAID driver (not included by default in XP, and I'm not positive about Vista). You have the same additional capabilities as AHCI like hot-swap and NCQ. You also have the added RAID support. This controller does not allow direct access to any device, but rather transforms the physical disks into logical RAID volumes. In order to access your storage, you must create RAID volumes, and those RAID volumes are exported to the operating system for access.

    I think the reason that you're not seeing your 250GB disk with XP on it is that the RAID controller sees the disk, but it is not part of a RAID volume so the operating system doesn't get to see it. Creating a RAID volume on the disk will likely destroy your data. You should try to connect it via a different SATA controller or maybe an external USB enclosure if you need access.
     
  4. Satsuki

    Satsuki Member

    Joined:
    Jan 5, 2009
    Messages:
    29
    Likes Received:
    0
    @MerlinRML
    First, thank you so much for actually providing GOOD information here on the AndandTech forums. I mostly get one liners or off topic B.S.

    So if I were to set up a new SATA HD I should run it in AHCI mode instead of SATA mode? Only if it has NCQ/Hot-swapping? Are there any other benefits to AHCI?

    Also, would a $30 RAID addon card be better than typical onboard controller? Do you have any suggestions? I'm not sure what chip I'm using.

    I'm running 2 x 500GB (Western Digital RE3) 128 stripe config, here are the results:

    http://img34.imageshack.us/img34/7514/captureiua.png

    Any configuration suggestions?

    Removed off topic content

    n7
    Memory/Storage Moderator
     
  5. MerlinRML

    MerlinRML Senior member

    Joined:
    Sep 9, 2005
    Messages:
    207
    Likes Received:
    0
    If you mean IDE/Legacy mode vs AHCI, then it's really hard to make a strong argument for one mode over the other unless there's a specific feature you need. IDE/Legacy is a more mature and supported mode, whereas AHCI is a newer, slightly better mode that isn't as well supported in all places. AHCI is more of where the future is going. Personally, I chose AHCI mode. Unless you're changing this regularly, I don't think it really matters that much.

    I don't believe a $30 RAID card would do much for you. First of all, those cards are likely to be driver based RAID, just like the AMD SB750 on your motherboard. Secondly, RAID 0 really doesn't require a lot of processing power so wouldn't benefit from an embedded RAID processor if the RAID card had one. Third, I don't know much about HDTune, bit judging from your performance numbers those look like sequential writes and are about where I would expect them to be. At the peak, you're getting about 109MB/sec for each drive and averaging about 87MB/sec which seems pretty close to where they should be.

    I'm hoping someone who's used HDTune with the 500GB RE3 drives can chime in if they're getting similar results.