Hello,
it's clear now. Thank you guys!
2016-01-27 10:22 GMT+01:00 Joao Eduardo Luis <joao@xxxxxxx>:
On 01/27/2016 08:58 AM, Sándor Szombat wrote:
> Hello,
>
> I'm testing ceph with minimal config on our servers (I'm using
> ceph-deploy tool). We have 3 monitor nodes with 6 OSD. The worst
> scenario when only 1 monitor and 2 osd up. Unfortunatelly in this case I
> got just error when I run for example ceph -s, I think it couldn't reach
> the cluster (I turned down the leader monitor). How can I config ceph to
> work with only 1 monitor? It is possible? I read this page
> <http://docs.ceph.com/docs/hammer/rados/configuration/mon-config-ref/>
> but this isn't clear exactly.
The monitors require a quorum to properly function. This means you need
a majority, of all the monitors in the monmap, participating in the
quorum. If you have 3 monitors in the monmap, you will always need at
least 2 of them up, running and participating in the quorum.
When you do not have a quorum, the monitors will stop handling client
requests. This is meant to guarantee consistency, via consensus, across
all the monitors.
The monitors elect the leader upon forming a quorum. Even if the
supposed leader is down, as long as you have a quorum you will always
have a leader. Of course, you will need 2 out of 3 monitors able to form
a quorum. If you don't have that, then you won't have a quorum, much
less a leader.
You can have just one monitor though, but that means you will have to
modify the monmap in order to have just one monitor in it. There are
ways to do this (check the docs, under "add/rm monitors"), but I don't
think that's what you want -- especially because you will lose all your
data if you lose your monitor. Except for test clusters, just one
monitor is definitely not advised.
Hope this helps.
-Joao
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