On Thu, 20 Jun 2013, Bo 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? Common misconception. * Ceph will work with any number of monitors. * Odd numbers are recommended. * Even numbers are not recommended becaus they tend to lower availability. Consider 2 mons: a majority (2) are needed to function, so now you have 2 points of failure instead of one and availability is worse. Split brain is not possible. sage > 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 > > >
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