Re: Very low disk performance Highpoint 1820a

From: Steven Hartland (killing_at_multiplay.co.uk)
Date: 04/29/05

  • Next message: kama: "Re: Very low disk performance Highpoint 1820a" 
    To: "Scott Long" <scottl@samsco.org>
Date: Fri, 29 Apr 2005 11:57:08 +0100

    ----- Original Message -----
    From: "Scott Long" <scottl@samsco.org>
    >> 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

    Just retried with a ~10Gb data set:
    Write to FS:
    dd if=/dev/zero of=.testfile bs=1m count=10000
    10000+0 records in
    10000+0 records out
    10485760000 bytes transferred in 92.517222 secs (113338466 bytes/sec)

    Read from FS:
    dd if=.testfile of=/dev/null bs=1m count=10000
    10000+0 records in
    10000+0 records out
    10485760000 bytes transferred in 225.723348 secs (46454034 bytes/sec)

    Read from device:
    dd if=/dev/da0 of=/dev/null bs=1m count=10000
    10000+0 records in
    10000+0 records out
    10485760000 bytes transferred in 200.723666 secs (52239779 bytes/sec)

    N.B. didn't do the write to the device direct as the array is
    the system drive so I don't think it would take kindly to that :)

    So it doesn't seem like caching is an issue and as others are seeing
    similar performance issues on other RAID controllers is could well
    not be a driver issue but I'm not ruling that out as yet as it could be
    the same problem in each respective driver.
    So far Highpoint 1820a and 3ware ?? ( Pete can u fill in the blank here )
    are exhibiting the same issue.

        Steve

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  • Next message: kama: "Re: Very low disk performance Highpoint 1820a"

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