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    SubjectRe: Linux 2.6.29
    David Rees wrote:
    > On Tue, Mar 24, 2009 at 12:32 AM, Jesper Krogh <> wrote:
    >> David Rees wrote:
    >> The 480 secondes is not the "wait time" but the time gone before the
    >> message is printed. It the kernel-default it was earlier 120 seconds but
    >> thats changed by Ingo Molnar back in september. I do get a lot of less
    >> noise but it really doesn't tell anything about the nature of the problem.
    >> The systes spec:
    >> 32GB of memory. The disks are a Nexsan SataBeast with 42 SATA drives in
    >> Raid10 connected using 4Gbit fibre-channel. I'll let it up to you to decide
    >> if thats fast or slow?
    > The drives should be fast enough to saturate 4Gbit FC in streaming
    > writes. How fast is the array in practice?

    Thats allways a good question.. This is by far not being the only user
    of the array at the time of testing.. (there are 4 FC-channel connected
    to a switch). Creating a fresh slice.. and just dd'ing onto it from
    /dev/zero gives:
    jk@hest:~$ sudo dd if=/dev/zero of=/dev/sdh bs=1M count=10000
    10000+0 records in
    10000+0 records out
    10485760000 bytes (10 GB) copied, 78.0557 s, 134 MB/s
    jk@hest:~$ sudo dd if=/dev/zero of=/dev/sdh bs=1M count=1000
    1000+0 records in
    1000+0 records out
    1048576000 bytes (1.0 GB) copied, 8.11019 s, 129 MB/s

    Watching using dstat while dd'ing it peaks at 220M/s

    If I watch numbers on "dstat" output in production. It gets at peak
    around the same(130MB/s) but average is in the 90-100 MB/s range.

    It has 2GB of battery backed cache. I'm fairly sure that when it was new
    (and I only had connected one host) I could get it up at around 350MB/s.

    >> The strange thing is actually that the above process (updatedb.mlocate) is
    >> writing to / which is a device without any activity at all. All activity is
    >> on the Fibre Channel device above, but process writing outsid that seems to
    >> be effected as well.
    > Ah. Sounds like your setup would benefit immensely from the per-bdi
    > patches from Jens Axobe. I'm sure he would appreciate some feedback
    > from users like you on them.
    >>> What's your vm.dirty_background_ratio and
    >>> vm.dirty_ratio set to?
    >> 2.6.29-rc8 defaults:
    >> jk@hest:/proc/sys/vm$ cat dirty_background_ratio
    >> 5
    >> jk@hest:/proc/sys/vm$ cat dirty_ratio
    >> 10
    > On a 32GB system that's 1.6GB of dirty data, but your array should be
    > able to write that out fairly quickly (in a couple seconds) as long as
    > it's not too random. If it's spread all over the disk, write
    > throughput will drop significantly - how fast is data being written to
    > disk when your system suffers from large write latency?

    Thats another thing. I havent been debugging while hitting it (yet) but
    if I go ind and do a sync on the system manually. Then it doesn't get
    above 50MB/s in writeout (measured using dstat). But even that doesn't
    sum up to 8 minutes .. 1.6GB at 50MB/s ..=> 32 s.


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