Quorum means you need at least %51 participating be it people following parliamentary procedures or mons in ceph. With one dead and two up you have %66 participating or enough to have a quorum. An even number doesn't get you any additional safety but does give you one more thing than can fail vs the next marginal odd number of mons. You can survive n failures if you have 2n+1 redundant systems.
On Jun 20, 2013, at 11:54 AM, Bo <b...@samware.com> wrote: > Howdy! > > Loving working with ceph; learning a lot. :) > > I am curious about the quorum process because I seem to get conflicting > information from "experts". Those that I report to need a clear answer from > me which I am currently unable to give. > > Ceph needs an odd number of monitors in any given cluster (3, 5, 7) to avoid > split-brain syndrome. So what happens whenever I have 3 monitors, 1 dies, and > I have 2 left? > > The information regarding this situation that I have gathered over the past > few months all falls within these three categories: > A) commonly "stated"--nothing is said. period. > B) rarely stated--this is a bad situation (possibly split-brain). > C) rarely stated--each monitor has a "rank", so the highest ranking monitor > is the boss, thus quorum. > > Does anyone know with absolute certainty what ceph's quorum logic will do > with an even number of (specifically 2) monitors left? > > You may say, "well, take down one of your monitors", to which I respectfully > state that my testing is not an authoritative answer on what ceph is designed > to do and what it does in production. My testing cannot cover the vast > majority of cases covered by the hundreds/thousands who have had a monitor > die. > > Thank you for your time and brain juice, > -bo > > > -- > > "But God demonstrates His own love toward us, in that while we were yet > sinners, Christ died for us. Much more then, having now been justified by His > blood, we shall be saved from the wrath of God through Him." Romans 5:8-9 > All have sinned, broken God's law, and deserve eternal torment. Jesus Christ, > the Son of God, died for the sins of those that will believe, purchasing our > salvation, and defeated death so that we all may spend eternity in heaven. Do > you desire freedom from hell and be with God in His love for eternity? > "If you confess with your mouth Jesus as Lord, and believe in your heart that > God raised Him from the dead, you will be saved." Romans 10:9 > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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