# [OmniOS-discuss] slog limits write speed more than it should

Bob Friesenhahn bfriesen at simple.dallas.tx.us
Fri Nov 14 14:47:47 UTC 2014

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    On Fri, 14 Nov 2014, Rune Tipsmark wrote:

    >
    > Looking at the first link he clearly states that ZIL is written to in a round robin fashion, I was under the
    > impression that 2 log devices would then be faster than 1…unless mirrored of course.

    This could be a mistaken impression.  The slog commits each write
    before proceeding to the next write.  If the involved SSDs have a
    fixed minimum write latency, then this would limit the maximum
    transaction rate regardless of the number of SSDs involved.  There
    could be an advantage to more SSDs if the additional time between
    writes allows the SSD to more effectively prepare for the next write
    and reduce the write latency.

    Bob
    --
    Bob Friesenhahn
    bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
    GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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