Is there a performance benifit using a RAID 0 configuration over a PCI Bus

Posted on 2006-03-27
Last Modified: 2010-04-26
I have recently purchased an HP a1350n AMD 64 x2 with a 250 GB SATA II hard drive.  I am using this machine for my main desktop and am looking for the best performance while using multiple "recourse and data intense" apps and large file read/write operations.  

The motherboard has two slots for SATA cables a PCI e and 3 PCI slots.  The second available SATA slot is for an additional drive for additional storage, there is not onboard RAID controller

I am currently using a multiple monitor setup that uses a gForce PCI e card and only have 1 of the 3 PCI slots available.  I have done some research on PCI cards that provide RAID solutions but have not been able to clearly determine if the read/write speeds would be better running RAID 0 through the PCI bus or just using a single HD connected to the SATA port on the motherboard.  The current HD is large enough for my needs and I would be willing to sacrifice the PCI e graphics card if it meant a "significant" speed gain by using a PCI e RAID controller card.  

Would a SATA II RAID 0 PCI or PCI e card solution (up to about $200 US) provide a significant performance increase?

Question by:rdilena
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    Expert Comment

    You need 2 physical hardrives to run RAID 0.  A hardware solution is what you are looking for.  PCI-e preferably.
    LVL 69

    Expert Comment

    The PCI bus is significantly slower when accessing hard drives, because the PCI bus is limited to 33MHz and is shared by all devices on the bus.  A connection directly connected to the motherboard will have a theoretical 150MHz limit for SATA1 and 300MHz for SATA2, though in reality it will be less because the hard drives can't deliver data that fast.  I tried a RAID-5 array with 4 SATA2 drives on a PCI slot and I saw only 40MB/sec throughput using HDTach.  A single drive hooked up directly to the motherboard can achieve 70MB/sec sustained.  A PCI-e connection would be better and could probably maintain the maximum throughput that the drives are capable of.

    Author Comment

    Callandor... Excellent thank you.  sounds like i should stay with my onboard connection or maybe the PCI e option.  Any Idea about the kind of speed gain (if any) possible using raid 0 on a pci e card and bus.
    LVL 69

    Expert Comment

    Using 2 WD Raptors in a RAID-0 array, I was able to achieve 100MB/sec sustained transfer rates connected to an MSI K8N Neo2 motherboard.  I had 2 7200rpm drives in a RAID-0 setup on another machine connected to the motherboard and got about 90MB/sec sustained.  I haven't tried PCI-e cards yet.
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    Expert Comment

    If you are utilizing the RAID for data, then you better off with a separate drive for your OS, and in your array 2 drives. That is a total of 3 drives. When you are searching for data, it won't be impeded by the OS.
    LVL 70

    Accepted Solution

    Well ... it's not quite so simple.

    First of all, SATA 150 and SATA 300 are NOT 150MHz and 300MHz clocks -- they're actually much faster than that ==> the 150/300 refers to the transfer rate in MB/s (the clock is more like 1.5GHz to clock all of the bits plus parity to achieve the 150MB/s transfer rate.).

    Second, the 33MHz PCI bus frequency results in data transfer rates about 132MB/sec, since the bus is 32-bits wide.   In fact, on server motherboards that have either 64-bit PCI slots or 66MHz PCI slots the transfer rate is double this; and on boards with 66MHz 64-bit PCI slots the rate is quadruple that !!
    (of course most systems don't use server motherboards)   Further, the overhead is very low if you're using a bus-mastering PCI RAID card -- since it takes over the PCI bus during its transfers.

    That's why the better RAID cards can achieve very nice transfer rates -- well over 100MB/s sustained rates.  Granted, a 33MHz 32-bit PCI slot is still limited to 132MB/s -- but that's a lot better than what was implied above.

    For MOST systems -- that aren't using the PCI bus extensively for other things -- a PCI RAID card will give very nice performance.    Clearly if you have a PCI-x slot available you can get even better performance; but remember that 132MB/s is an outstanding SUSTAINED rate.   Unless you have more than 2 drives in a RAID-0 array, that's probably about as fast as you're going to achieve with ANY controller.   I think you'd be very satisfied with a good (e.g. 3ware) PCI controller and a nice pair of high-performance drives (e.g. Raptors).
    LVL 69

    Expert Comment

    Oops - Gary is right, my feeble mind was comparing SATA's 150MB/sec transfer rate with the ATA133 spec, which is basically apples and oranges.  However, my data was obtained from a HighPoint 1820A PCI-X card, which isn't in the same league as 3Ware cards, but does fit the $200 limit.  If you go with 3Ware, be prepared to spend $300 and up, perhaps $500.

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