On Aug 21, 2009, at 5:55 PM, Tim Cook wrote:
On Fri, Aug 21, 2009 at 7:41 PM, Richard Elling <richard.ell...@gmail.com
> wrote:
My vote is with Ross. KISS wins :-)
Disclaimer: I'm also a member of BAARF.
My point is, RAIDZx+1 SHOULD be simple. I don't entirely understand
why it hasn't been implemented. I can only imagine like so many
other things it's because there hasn't been significant customer
demand. Unfortunate if it's as simple as I believe it is to
implement. (No, don't ask me to do it, I put in my time programming
in college and have no desire to do it again :))
You can get in the same ballpark with at least two top-level raidz2
devs and
copies=2. If you have three or more top-level raidz2 vdevs, then you
can even
do better with copies=3 ;-)
Note that I do not have a model for that because it would require
separate
failure rate data for whole disk failures and all other non-whole disk
failures.
The latter is not available in data sheets. The closest I can get with
published
data is using the MTTDL[2] model which considers the published
unrecoverable
read error rate. In other words, the model would be easy, but data to
feed the
model is not available :-( Suffice to say, 2 top-level raidz2 vdevs
of similar size
with copies=2 should offer very nearly the same protection as raidz2+1.
-- richard
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