Re: dd(1) performance when copiing a disk to another

From: Tulio Guimarăes da Silva (tuliogs_at_pgt.mpt.gov.br)
Date: 10/03/05

  • Next message: Tulio Guimarăes da Silva: "Re: dd(1) performance when copying a disk to another" 
    Date: Mon, 03 Oct 2005 11:57:14 -0300
To: freebsd-performance@freebsd.org

    Steven Hartland wrote:

    > ----- Original Message ----- From: "Arne Wörner" <arne_woerner@yahoo.com>
    >
    >> That seems to be 2 or about 2 times faster than disc->disc
    >> transfer... But still slower, than I would have expected...
    >> SATA150 sounds like the drive can do 150MB/sec...
    >
    >
    > LOL, you might want to read up on what SATA150 means.
    > In short it the max throughput the interface can sustain. It is NOT
    > what you can get of a single disk which is still fare from that,
    > SATA disk transfer rates typically 30 -> 50MB/s sustained.
    >
    > Steve

      Indeed. In other words, that represents the max transfer rates between
    the SATA controller and the disk´s controller (at best, you´ll get close
    to it when reading from the disk´s onboard cache), but the media will
    always be much slower.
      But just to clear out some questions...
      1) Maxtor´s full specifications for Diamond Max+ 9 Series refers to
    maximum *sustained* transfer rates of 37MB/s and 67MB/s for "ID" and
    "OD", respectively (though I couldn´d find exactly what it means, I
    deduced that represents the rates for center- and border-parts of the
    disk - please correct me if I´m wrong), then your tests show you´re
    getting the best out of it ;) ;
      2) Mr. Hartland mentioned the numbers to be good for a single drive,
    therefore it´s a bit better for a disk-to-disk, where the limit should
    be the slower disk´s performance. I couldn´t look for the specs of the
    Toshiba since I didn´t have the exact model, but I would expect it to be
    equal or faster than the Maxtor, since it does not appear to be a
    bottleneck.

      One last thought, though, for the specialists: iostat showed maximum
    of 128KB/transfer, even though dd should be using 1MB blocks... is that
    an expected behaviour? Shouldn´t iostat show 1024Kb/t, then?
      Thanks for your attention,

    Tulio G. da Silva

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