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

From: Willem Jan Withagen (wjw_at_withagen.nl)
Date: 10/13/05

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    Date: Thu, 13 Oct 2005 02:14:11 +0200
To: Bruce Evans <bde@zeta.org.au>

    Bruce Evans wrote:
    > On Mon, 3 Oct 2005, [ISO-8859-1] Tulio Guimar�es da Silva wrote:
    >
    >> 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 ;) ;
    >> much slower.
    >
    >
    > Another interesting point is that you can often get closer to the maximum
    > rate than the average of the maximum and minumum rate. The outer tracks
    > contain more sectors (about 67/37 times as many with the above spec), so
    > the average rate over all sectors is larger than average of the max and
    > min,
    > significantly so since 67/37 is a fairly large fraction. Also, you can
    > often partition disks to put less-often accessed stuff in the slow parts.
    >

    [All GEOM alligning deleted]

    As it so happens, I have again some (faster) spare servers in my office.
    And given the NFS-tests of last year, I want to see if I could run those
    tests again. But before doing so I wanted to verify the extent of what Bruce
    suggest here above. (Which I found first in an article some time ago)

    I've written a small, not yet complete page, on the topic. At current it only
    involves writting to the disk. But it clearly visualises the effect of
    non-constant transferrates, which actually depends on the location of the
    track read from.

    If you want, you could see for yourself at:
            http://withagen.dyndns.org/FreeBSD/Performance/Raw-disk/
    Suggestions etc. are welcome.

    --WjW
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