On Fri, Aug 21, 2009 at 5:52 PM, Ross Walker <rswwal...@gmail.com> wrote:
> On Aug 21, 2009, at 6:34 PM, Tim Cook <t...@cook.ms> wrote: > > > > On Fri, Aug 21, 2009 at 5:26 PM, Ross Walker < <rswwal...@gmail.com> > rswwal...@gmail.com> wrote: > >> On Aug 21, 2009, at 5:46 PM, Ron Mexico < <no-re...@opensolaris.org> >> 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. > > > If that is the case how about a separate zpool of large SATA disks and > either snapshot and send/recv to it, or use AVT to replicate to it. > That adds a window of opportunity for failure. Potentially quite a large window. > > > > >> >> 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. > > > > It's not worth the cost, the complexity is so high that it itself will be a > point of failure and performance is too low for it to be any use. > > The complexity? There should be no complexity involved in a mirrored raid-z/z2 pool. > > > > >> 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 > > > 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. > > > > Setup a side raidz2 zpool of SATA disks, snap the RAID10 and zsend it to > the other pool. In the event of catastrophy you can run off the raidz2 pool > temporarily until the mirror pool is fixed (and it would still perform > better then the mirrored raidz2 setup!). > > Snapshots are not a substitute for raid. That's a completely different protection mechanism. If he wants another copy of the data, I'm sure he'll setup a second server and do zfs send/receives.
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