> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
> boun...@opensolaris.org] On Behalf Of Bob Friesenhahn
> Has someone done real-world measurements which indicate that raidz*
> actually provides better sequential read or write than simple
> mirroring with the same number of disks?  While it seems that there
> should be an advantage, I don't recall seeing posted evidence of such.
> If there was a measurable advantage, it would be under conditions
> which are unlikely in the real world.

Apparently I pulled it down at some point, so I don't have a URL for you
anymore, but I did, and I posted.  Long story short, both raidzN and mirror
configurations behave approximately the way you would hope they do.  That

Approximately, as compared to a single disk:  And I *mean* approximately,
because I'm just pulling it back from memory the way I chose to remember it,
which is to say, a simplified model that I felt comfortable with:
                seq rd  seq wr  rand rd rand wr
2-disk mirror   2x      1x      2x      1x
3-disk mirror   3x      1x      3x      1x
2x 2disk mirr   4x      2x      4x      2x
3x 2disk mirr   6x      3x      6x      3x
3-disk raidz    2x      2x      1x      1x
4-disk raidz    3x      3x      1x      1x
5-disk raidz    4x      4x      1x      1x
6-disk raidz    5x      5x      1x      1x

I went on to test larger and more complex arrangements...  Started getting
things like 1.9x and 1.8x where I would have expected 2x and so forth...
Sorry for being vague now, but the data isn't in front of me anymore.  Might
not ever be again.

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