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    SubjectRe: Poor performance during disk writes


    On Tue, 18 Dec 2001, Andre Hedrick wrote:

    > File './Bonnie.2276', size: 1073741824, volumes: 1
    > Writing with putc()... done: 72692 kB/s 83.7 %CPU
    > Rewriting... done: 25355 kB/s 12.0 %CPU
    > Writing intelligently...done: 103022 kB/s 40.5 %CPU
    > Reading with getc()... done: 37188 kB/s 67.5 %CPU
    > Reading intelligently...done: 40809 kB/s 11.4 %CPU
    > Seeker 2...Seeker 1...Seeker 3...start 'em...done...done...done...
    > ---Sequential Output (nosync)--- ---Sequential Input-- --Rnd Seek-
    > -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --04k (03)-
    > Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
    > 1*1024 72692 83.7 103022 40.5 25355 12.0 37188 67.5 40809 11.4 382.1 2.4
    >
    > Maybe this is the kind of performance you want out your ATA subsystem.
    > Maybe if I could get a patch in to the kernels we could all have stable
    > and fast IO.

    I rather see lots of wasting rather than performance, here. Bonnie says
    that your subsystem can sustain 103 MB/s write but only 41 MB/s read. This
    looks about 60% throughput wasted for read.

    Note that if you intend to use it only for write-only applications,
    performance are not that bad, even if just dropping the data on the floor
    would give you infinite throughput without any difference in
    functionnality. :-)


    Gérard Roudier
    Not CEO, not President of anything.

    > Regards,
    >
    >
    > Andre Hedrick
    > CEO/President, LAD Storage Consulting Group
    > Linux ATA Development
    > Linux Disk Certification Project

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