On Mon, 28 Jul 2014 11:22:38 +0100 Joao Eduardo Luis wrote: > On 07/28/2014 08:49 AM, Christian Balzer wrote: > > > > Hello, > > > > On Sun, 27 Jul 2014 18:20:43 -0400 Robert Fantini wrote: > > > >> Hello Christian, > >> > >> Let me supply more info and answer some questions. > >> > >> * Our main concern is high availability, not speed. > >> Our storage requirements are not huge. > >> However we want good keyboard response 99.99% of the time. We > >> mostly do data entry and reporting. 20-25 users doing mostly > >> order , invoice processing and email. > >> > >> * DRBD has been very reliable , but I am the SPOF . Meaning that > >> when split brain occurs [ every 18-24 months ] it is me or no one who > >> knows what to do. Try to explain how to deal with split brain in > >> advance.... For the future ceph looks like it will be easier to > >> maintain. > >> > > The DRBD people would of course tell you to configure things in a way > > that a split brain can't happen. ^o^ > > > > Note that given the right circumstances (too many OSDs down, MONs down) > > Ceph can wind up in a similar state. > > > I am not sure what you mean by ceph winding up in a similar state. If > you mean regarding 'split brain' in the usual sense of the term, it does > not occur in Ceph. If it does, you have surely found a bug and you > should let us know with lots of CAPS. > > What you can incur though if you have too many monitors down is cluster > downtime. The monitors will ensure you need a strict majority of > monitors up in order to operate the cluster, and will not serve requests > if said majority is not in place. The monitors will only serve requests > when there's a formed 'quorum', and a quorum is only formed by (N/2)+1 > monitors, N being the total number of monitors in the cluster (via the > monitor map -- monmap). > > This said, if out of 3 monitors you have 2 monitors down, your cluster > will cease functioning (no admin commands, no writes or reads served). > As there is no configuration in which you can have two strict > majorities, thus no two partitions of the cluster are able to function > at the same time, you do not incur in split brain. > I wrote similar state, not "same state".
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