Re: Very low disk performance Highpoint 1820a

From: Scott Long (scottl_at_samsco.org)
Date: 04/29/05

  • Next message: Petri Helenius: "Re: Very low disk performance Highpoint 1820a" 
    Date: Fri, 29 Apr 2005 02:26:50 -0600
To: Steven Hartland <killing@multiplay.co.uk>

    Steven Hartland wrote:
    > Scott I've sent this to you as from reading around you did the
    > original driver conversion and as such may have an idea
    > on the areas I could look at hope you dont mind.
    >
    > Ok some real strange going on write performance is ~ 140MB/s:
    > gstat:
    > dT: 0.505 flag_I 500000us sizeof 240 i -1
    > L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name
    > 0 1100 4 63 13.2 1096 140313 1.2 57.8| da0
    > 0 1100 4 63 13.3 1096 140313 1.3 59.3| da0s1
    >
    > where as read is ~42MB/s
    > gstat:
    > dT: 0.505 flag_I 500000us sizeof 240 i -1
    > L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name
    > 1 335 335 42836 2.8 0 0 0.0 93.3| da0
    > 1 335 335 42836 2.8 0 0 0.0 93.6| da0s1
    >

    First of all, you're only sending roughly 3GB of data through. Since
    you have 2GB of RAM, you're likely getting a lot of write caching
    from the OS. If you want more representative numbers, either test
    with a much larger data set or with a much smaller RAM size. Second,
    since you're going through the filesystem, there is a very good chance
    that the filesystem blocks are not aligning well with the array
    blocks. This hurts quite a bit on any controller, and I can imagine
    it being extremely bad on a controller like this one. Try doing your
    DD test straight to the device node. In my local testing I was able to
    get about 400MB/sec across 6 disks in RAID-0. RAID-5 read should
    get almost as good in a similar configuration (unless the RAID stack
    is checking parity on read, a question that I cannot answer). I would
    expect RAID-5 write to be significantly lower due to the extra cpu and
    memory bus overhead of doing the parity calculations. This will of
    course depend also on the speed of your drives and the speed of your PCI
    and memory bus.

    The DD commands that I usually use:

    dd if=/dev/zero of=/dev/da0 bs=1m
    dd if=/dev/da0 of=/dev/null bs=1m
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