# [OmniOS-discuss] zfs pool 100% busy, disks less than 10%

Richard Elling richard.elling at richardelling.com
Mon Nov 3 19:31:49 UTC 2014

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    [responding to myself, considering the audience]

    On Nov 3, 2014, at 11:30 AM, Richard Elling <richard.elling at richardelling.com> wrote:

    >
    > On Nov 2, 2014, at 6:24 PM, Rune Tipsmark <rt at steait.net> wrote:
    >
    >> Looking a bit more at these numbers, am I seeing twice the actual rate due to mirroring?
    >
    > You need to know what you are measuring. iostat and zpool iostat measure the I/O from
    > the pool to the disk. This is often very different than an application to the file system (pool).
    > In practice, it is often so different that it is impractical to correlate the two.
    >
    >> How does compression affect the numbers?
    >>
    >> Say I have 1 vdev mirrored and I see the pool writing 100 MB/sec, its what? 50 MB each disk? But from the client side only 50 MB/sec total? What if I compress it at the same time at say 1.50 ratio, will the pool show 100 MB/sec and the client write 75 MB/sec actual?
    >
    > Measure both and compare. Usually we measure application side bandwidth using a tool
    > such as fsstat.

    actually, we measure it using some sort of data collector that stores data for long-term
    analysis and includes handy graphing features (cue Circonus)
     -- richard

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