What's reasonable RAID 5 performance?

Discussion in 'Storage' started by kenw, Sep 6, 2004.

  1. kenw

    kenw Guest

    I have a nice new server with 15,000RPM SCSI drives in a hardware RAID 5
    configuration. I may be wrong, but I don't think it's performing properly
    at all. The question is, what's reasonable?

    When using large (>500MB) files to swamp out cache effects, I'm getting
    roughly 12MB/sec (it varies quite a bit) write performance and maybe 200
    MB/sec, when measured with IOzone.

    Measuring with batch 'copy' commands, I'm getting 40MB/sec read-only (copy
    to NUL:) and about 14MB/sec copying back to the same array. One of the
    challenges has been getting consistent results; not sure why.

    These numbers strike me as being OTL (out to lunch) for such
    high-performance drives and array controller.

    The array consists of five Seagate Cheetah ST336753LC 15,000RPM drives
    connected via a 320MB/sec SCSI interface. The controller is an Intel
    SRCU42X as provided by Intel, i.e., the standard 128MB cache, and no
    on-board battery (the server has a UPS and redundant power supplies
    connected to separate power sources) which means the controller will do
    write-through, but not write-back, caching. No override is available.

    Intel claims that this is the optimum configration for the controller, and
    that more RAM or the battery pack will not help performance significantly.
    The motherboard, BTW, is an Intel SE7501HG2 with dual 2.8GHz Xeons and 2GB
    of RAM.

    There must be thousands of RAID 5 arrays out there very similar to this
    one. _Somebody_ must know. Are these performance figures reasonable, or
    Ken Wallewein
    K&M Systems Integration
    Phone (403)274-7848
    Fax (403)275-4535

    kenw, Sep 6, 2004
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  2. kenw

    Arno Wagner Guest

    One data-point: On a software RAID5 with 2.6.7 and 5 * Maxtor
    200GB DiamondMax 9 plus I get 22MB/s large file write performance
    (measured with 1GB data file) and 65MB/s read performance. That is with
    ext3 journalling file system, which also journals data, not only
    I would say the performance is rather embarassing when a software
    RAID on half as fast disks performs massively better. However I
    recenly made the mistake of buying an adaptec SATA RAID controller.
    Also slower than software RAID. I also recently talked to some
    guy running huge usenet servers: They also have noted that hardware
    RAID is now slower than software RAID. As soon as Linux supports
    ATA/SATA hotplugging the last advantage of hardware RAID will
    be gone.

    Arno Wagner, Sep 6, 2004
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  3. kenw

    Ron Reaugh Guest

    Gigabit isn't fast enough here.
    Ron Reaugh, Sep 7, 2004
  4. kenw

    Ron Reaugh Guest

    Some HW RAID may be slower but not the right stuff configured properly. SW
    RAID is moving in on most the territories though.
    Ron Reaugh, Sep 7, 2004
  5. kenw

    Rob Turk Guest

    If your 12MB/s is really what you get, then flushing your 128MB cache takes
    10 seconds. If some idiot decides to push the power button on the server, it
    will switch off before your cache is flushed. Maybe not such a bad idea to
    get the battery option anyway??

    Rob Turk, Sep 7, 2004
  6. kenw

    kenw Guest

    Sure it is. It's far faster than the throughput I'm getting from the array
    right now, and faster than a 32-bit PCI bus (the RAID server's 64). As it
    happens, the only system I currently have to trade files with has a 32bit
    PCI, and when I watch network utilization, the bottleneck is obvious.

    A gigabit network should be able to approach 100MB/sec -- say, at least 80.
    If I was getting that from my RAID array, I'd be happy.

    BTW, the copy append idea in Eric's message is a great idea. It
    effectively lets me do write-only write performance testing, almost the
    reverse of my copy-to-NUL read test. Cool!

    Unfortunately, none of this either confirms or denies whether my current
    RAID 5 performance is reasonable.

    Ken Wallewein
    K&M Systems Integration
    Phone (403)274-7848
    Fax (403)275-4535

    kenw, Sep 7, 2004
  7. kenw

    Ron Reaugh Guest

    You just contradicted yourself overall. Your stated goal is "should be
    getting". For that gigabit is NOT fast enough. What about the 200?
    No, gigabit is about the same speed at peak of 32 bit 33 Mhz PCI.
    Rethink what you are watching.

    That's what I've said and 32 bit 33.3 Mhz PCI does 133.3 MB/sec.
    What about the 200?
    Ron Reaugh, Sep 7, 2004
  8. Oh?
    What about the "the controller will do write-through, but not write-back, caching"?
    Folkert Rienstra, Sep 7, 2004
  9. kenw

    Ron Reaugh Guest


    Read the thread before blathering. The controller WILL do write-back when
    it has a battery.
    Ron Reaugh, Sep 7, 2004
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