On Aug 21, 2009, at 3:34 PM, Tim Cook wrote:
On Fri, Aug 21, 2009 at 5:26 PM, Ross Walker <rswwal...@gmail.com>
wrote:
On Aug 21, 2009, at 5:46 PM, Ron Mexico <no-re...@opensolaris.org>
wrote:
I'm in the process of setting up a NAS for my company. It's going to
be based on Open Solaris and ZFS, running on a Dell R710 with two
SAS 5/E HBAs. Each HBA will be connected to a 24 bay Supermicro JBOD
chassis. Each chassis will have 12 drives to start out with, giving
us room for expansion as needed.
Ideally, I'd like to have a mirror of a raidz2 setup, but from the
documentation I've read, it looks like I can't do that, and that a
stripe of mirrors is the only way to accomplish this.
Why?
Because some people are paranoid.
cue the Kinks Destroyer :-)
It uses as many drives as a RAID10, but you loose 1 more drive of
usable space then RAID10 and you get less then half the performance.
And far more protection.
Yes. With raidz3 even more :-)
I put together a spreadsheet a while back to help folks make this sort
of decision.
http://blogs.sun.com/relling/entry/sample_raidoptimizer_output
I didn't put the outputs for RAID-5+1, but RAIDoptmizer can calculate
it.
It won't calculate raidz+1 because there is no such option. If there
is some
demand, I can put together a normal RAID (LVM or array) output of
similar
construction.
You might be thinking of a RAID50 which would be multiple raidz
vdevs in a zpool, or striped RAID5s.
If not then stick with multiple mirror vdevs in a zpool (RAID10).
-Ross
My vote is with Ross. KISS wins :-)
Disclaimer: I'm also a member of BAARF.
Raid10 won't provide as much protection. Raidz21, you can lose any
4 drives, and up to 14 if it's the right 14. Raid10, if you lose
the wrong two drives, you're done.
One of the reasons I wrote RAIDoptimizer is to help people get a
handle on the math behind this. You can see some of that orientation
in my other blogs on MTTDL. But at the end of the day, you can get a
pretty good ballpark by saying every level of parity adds about 3 orders
of magnitude to the MTTDL. No parity is always a loss. Single parity
is better. Double parity even better. Eventually, common-cause problems
dominate.
-- richard
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