> 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
is...
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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