Re: Very low disk performance on 5.x

From: Poul-Henning Kamp (phk_at_phk.freebsd.dk)
Date: 05/02/05

  • Next message: Bakul Shah: "Re: Very low disk performance on 5.x"
    To: "Steven Hartland" <killing@multiplay.co.uk>
    Date: Mon, 02 May 2005 19:33:18 +0200
    
    

    In message <003901c54f36$0c64ad40$b3db87d4@multiplay.co.uk>, "Steven Hartland"
    writes:

    >Ok from what your saying it sounds like RAID on FreeBSD is useless
    >apart to create large disks. Now to the damaging facts the results
    >from my two days worth of testing:

    Now, cool down a moment and lets talk about what you _really_ have
    measured.

    You have measured the end to end performance: you include /dev/zero,
    dd(1), filesystem, disk device driver, hardware and disks.

    As such that is a fair end-user benchmark, but unfortunately it
    doesn't really tell us anything useful for the purpose of this
    discussion.

    If you are going to do a high-performance setup, you should not
    just take the "out-of-box" settings, you should optimize for
    the configurations particular features.

    Testing end-to-end means that we have very little to go from to
    find out where things went wrong in any one instance.

    But anyway: here are some questions which I wonder about ?

    Does the linux and FreeBSD filesystem offer the same semantics
    with respect to integrity ? Ie: if one is asyncronous mode
    the comparison is not a fair comparison. Just because you
    chose the default in each case doesn't mean you got the same
    thing.

    Does any of the drivers change the settings/modes of the controllers
    use of cache ? (this may be hard to determine without looking
    at driver sources.

    In particular, are you sure that the RAID-5 logical device was
    in the same exact state and location for each run ?

    Did you remember to disable all the debugging in FreeBSD 6-Current ?
    (see top of src/UPDATING)

    -- 
    Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
    phk@FreeBSD.ORG         | TCP/IP since RFC 956
    FreeBSD committer       | BSD since 4.3-tahoe    
    Never attribute to malice what can adequately be explained by incompetence.
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  • Next message: Bakul Shah: "Re: Very low disk performance on 5.x"

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