On Sep 16, 2009, at 12:50 PM, Marty Scholes wrote:
This line of reasoning doesn't get you very far.
It is much better to take a look at<br>
the mean time to data loss (MTTDL) for the various
configurations. I wrote a<br>
series of blogs to show how this is done.<br>
<a href="http://blogs.sun.com/relling/tags/mttdl"; target="_blank">http://blogs.sun.com/relling/tags/mttdl
</a><br><br>
I will play the Devils advocate here and point out that the chart
shows MTTDL for RAIDZ2, both 6 and 8 disk, is much better than
mirroring.
The chart does show that three way mirroring is better still and I
would guess that RAIDZ3 surpasses that.
Yes. This is a mathematical way of saying "lose any P+1 of N disks."
The important part is that the number of parity disks (or mirror sides)
is the big knob to use. But every choice is a trade-off. For a single
set, the results should be intuitive. But as you vary the number of
sets,
it quickly becomes easier to use the models. For example, with a
Thumper, you have 48 disks and zillions of possible combinations
to choose from.
-- richard
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