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  1. #1
    Just Joined!
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    Jun 2003
    Elmore Co., AL USA

    Question RAID impact on u-processor load?

    I am considering a new computer with mobo with onboard RAID 1 controller (Intel). The RAID 1 would be two identical SATA-2 drives.

    I am considering the E6550 or maybe E8200 because they are nicely priced and very capable as packaged with the system.

    I have not considered the Q9300 because for the money, I don't see that much benefit ---


    unless the load of RAID will impact the processor. This computer will be used as an individual desktop computer and not as a server.

    I have used RAID on servers but there was always a RAID controller and I never thought the processor much cared what was going on since the controller had its own cache, etc.

    With RAID on board should I lean toward the quad or will the onboard processor take care of things without significant impact on processor load. Likely the computer will never see heavy use anyway -- whole project is overkill to the nth degree, but I'd like to do the better thing.


  2. #2
    Just Joined!
    Join Date
    Jun 2003
    Elmore Co., AL USA

    Exclamation Question answered -- I think.

    The answer to my question is contained in two sections of Wikipedia's discussion of RAID.

    I won't paste the entire text here because there are probably copyright implications to doing that. But, I will link to the RAID page at Wikipedia and include some excerpts below. RAID - Wikipedia, the free encyclopedia

    .... A hardware implementation of RAID requires at least a special-purpose RAID controller. On a desktop system this may be a PCI expansion card, PCI-e expansion card or built into the motherboard. .... The controller hardware handles the management of the drives, and performs any parity calculations required by the chosen RAID level.

    Most hardware implementations provide a read/write cache which, depending on the I/O workload, will improve performance. In most systems the write cache is non-volatile (i.e. battery-protected), {emphasis added} so pending writes are not lost on a power failure.

    Hardware implementations provide guaranteed performance, add no overhead to the local CPU complex and can support many operating systems, as the controller simply presents a logical disk to the operating system. ....

    Firmware/driver based RAID
    .... Hardware RAID controllers are expensive. To fill this gap cheap "RAID controllers" were introduced that do not contain a RAID controller chip, but simply a standard disk controller chip with special firmware and drivers. ....

    These controllers are described by their manufacturers as RAID controllers, and it is rarely made clear to purchasers that the burden of RAID processing is borne by the host computer's central processing unit, not the RAID controller itself, {emphasis added} thus introducing the aforementioned CPU overhead. Before their introduction, a "RAID controller" implied that the controller did the processing, and the new type has become known in technically knowledgeable circles as "fake RAID" even though the RAID itself is implemented correctly.
    So now I must determine whether the motherboard I am considering has a RAID controller or not. Looking at pictures, there is no indication of a RAID controller in parts layouts. Another clue is there is no battery for maintaining a write-cache in the event of a power failure.

    Therefore, I have concluded there will be processor load for RAID and I will make my processor selection decision with that in mind. Because the computer will not be heavily used, I may stick with the E (dual core) because of the cost saving and lack of current applications calling for quad cores. But at least I will know what I am dealing with.

    Hope this helps someone else.

  3. #3
    Unless the mobo is several hundred dollars (and not $200 or less as most boards are), it won't be a "true" RAID controller with it's own processor.

    However, this is not too much of a concern. When CPU's were 200MHz a dedicated proc for RAID calculations would make a difference under load.

    Now we have 2.8GHz CPU's and RAID procs that are typically 133-200MHz. See the difference? That RAID doesn't make a big hit on the modern CPU.

    Also consider the load that different RAID config's create - calculating the XOR bit for a RAID 5 set is one thing, but a RAID 1 is a mirror. Data is sent to two drives instead of one - there is no calculation involved, so a software mirror would have little impact on a modern CPU.

    There are other pros/cons to a separate, HW controller (cost, cache, battery), but these seem to be what you're focused on.

    there is no indication of a RAID controller in parts layouts
    The "software" RAID is implemented (at this time) by the SATA controller and the driver in the OS (hence the "software" part of the name.)


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