On Fri, Aug 21, 2009 at 7:41 PM, Richard Elling <richard.ell...@gmail.com>wrote:
> 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. Good point as well. Completely spaced on the fact raidz3 was added not so long ago. I don't think it's made it to any officially supported build yet though, has it? > > > 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. 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 :)) > > > 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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