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    SubjectRe: io-scheduler tuning for better read/write ratio
    Jeff Moyer schrieb:
    > Jeff Moyer <jmoyer@redhat.com> writes:
    >
    > > Ralf Gross <rg@stz-softwaretechnik.com> writes:
    > >
    > >> Casey Dahlin schrieb:
    > >>> On 06/16/2009 02:40 PM, Ralf Gross wrote:
    > >>> > David Newall schrieb:
    > >>> >> Ralf Gross wrote:
    > >>> >>> write throughput is much higher than the read throughput (40 MB/s
    > >>> >>> read, 90 MB/s write).
    > >>> >
    > >>> > Hm, but I get higher read throughput (160-200 MB/s) if I don't write
    > >>> > to the device at the same time.
    > >>> >
    > >>> > Ralf
    > >>>
    > >>> How specifically are you testing? It could depend a lot on the
    > >>> particular access patterns you're using to test.
    > >>
    > >> I did the basic tests with tiobench. The real test is a test backup
    > >> (bacula) with 2 jobs that create 2 30 GB spool files on that device.
    > >> The jobs partially write to the device in parallel. Depending which
    > >> spool file reaches the 30 GB first, one starts reading from that file
    > >> and writing to tape, while to other is still spooling.
    > >
    > > We are missing a lot of details, here. I guess the first thing I'd try
    > > would be bumping up the max_readahead_kb parameter, since I'm guessing
    > > that your backup application isn't driving very deep queue depths. If
    > > that doesn't work, then please provide exact invocations of tiobench
    > > that reprduce the problem or some blktrace output for your real test.
    >
    > Any news, Ralf?

    sorry for the delay. atm there are large backups running and using the
    raid device for spooling. So I can't do any tests.

    Re. read ahead: I tested different settings from 8Kb to 65Kb, this
    didn't help.

    I'll do some more tests when the backups are done (3-4 more days).

    Thanks, Ralf



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