I have my testcluster consisting two OSDs that also host MONs plus
one to five MONs.
Are you saying that you have a total of 7 mons?
yepp
down the at last, not the other MON though (since - surprise - they
are in this test szenario just virtual instances residing on some
ceph rbds)
This seems to be your problem. When you shutdown the cluster, you
haven't got those extra mons.
In order to reach a quorum after reboot, you need to have more than half
of yours mons running.
wait!
lets say in my setup (which might be silly giving the MON / OSD ratio but still)
with 7 MONs I have to have at least 5 MONS running?
4 would be more than the half but insufficient to reach a quorum.
But, would the cluster come up at all if I could get only 3 out of the 7 initial MONs up and running?
If you have 5 or more mons in total, this means that the two physical
servers running mons cannot reach quorum by themselves.
I.e. you have 2 mons out of 5 running for example - it will not reach a
quorum because you need at least 3 mons to do that.
Well, as I said, I had 3 MONs running, just the sequence in which they came up after the reboot was odd,
first the first MON/OSD combination came to life, than a second MON, than the second MON/OSD combination
You need to either move mons to physical machines, or virtual instances
not depending on the same Ceph cluster, or reduce the number of mons in
the system to 3 (or 1).
And do I need to make sure that a quorum capable number of MONs is up BEFORE I restart the OSDs?
than the sequence would be:
- free cluster of load/usage
- stop MDS / any given order
- stop OSD / any given order
- stop MON / one after the other
- start MON / in reverse order, last shutdown is first boot
- start OSD
- start MDS
- allow load to the cluster again
central question remains, do I need 5 out of 7 MONs running or would 3 out of 7 be sufficient?
TIA
Bernhard
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Bernhard Glomm IT Administration
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