On Thu, Aug 2, 2012 at 8:22 PM, Benoît Canet <benoit.ca...@irqsave.net> wrote: >> I'm not entirely sure I understand the use-case all that well. >> >> Wouldn't the more typical approach be RAID-5 and the use of parity >> instead of relying on voting? >> >> Quorum doesn't work well with an odd number of disks whereas RAID-5 >> does. You also get significantly more usable disk space with RAID-5 >> then with voting. >> > > Hello, > > Use case: > > A customer using NFS want to setup redudancy across multiple separate > rooms of the same datacenter. > In this case only the network is common. > > Testing prove that synchronisation between high end storage applicances > fail in this case. > Something else is required. > > With raid5 a small network glitch between the hypervisor and one > of the filer can bring down a while md raid-5 disk. > This involve a rebuild of this disk using heavy parity computation. > (imagine the load with many disk images) > Properly done qorum will correct the error on the fly. > > Quorum can correct bitflips induced by the network raid5 cannot. > (bad case ethernet cable sitting around power cord) > > Quorum require only two read out of three to reach majority in the > best case. > > Some well known cloud provider already use quorum in their setup
There is discussion about adding end-to-end data integrity checks to NFSv4: http://www.ietf.org/proceedings/83/slides/slides-83-nfsv4-2.pdf This doesn't seem to exist yet but I wanted to share the slides. Stefan
