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Merge pull request ceph#58057 from zdover23/wip-doc-2024-06-15-rados-…
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doc/rados: explain replaceable parts of command

Reviewed-by: Anthony D'Atri <[email protected]>
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zdover23 authored Jun 16, 2024
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28 changes: 16 additions & 12 deletions doc/rados/troubleshooting/troubleshooting-mon.rst
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Expand Up @@ -133,10 +133,14 @@ Understanding mon_status

The status of a Monitor (as reported by the ``ceph tell mon.X mon_status``
command) can be obtained via the admin socket. The ``ceph tell mon.X
mon_status`` command outputs a great deal of information about the monitor
mon_status`` command outputs a great deal of information about the monitor
(including the information found in the output of the ``quorum_status``
command).

.. note:: The command ``ceph tell mon.X mon_status`` is not meant to be input
literally. The ``X`` portion of ``mon.X`` is meant to be replaced with a
value specific to your own Ceph cluster when you run the command.

To understand this command's output, let us consider the following example, in
which we see the output of ``ceph tell mon.c mon_status``::

Expand Down Expand Up @@ -165,24 +169,24 @@ which we see the output of ``ceph tell mon.c mon_status``::
"name": "c",
"addr": "127.0.0.1:6795\/0"}]}}

This output reports that there are three monitors in the monmap (*a*, *b*, and
*c*), that quorum is formed by only two monitors, and that *c* is in quorum as
a *peon*.
This output reports that there are three monitors in the monmap (``a``, ``b``,
and ``c``), that quorum is formed by only two monitors, and that ``c`` is in
quorum as a ``peon``.

**Which monitor is out of quorum?**

The answer is **a** (that is, ``mon.a``). ``mon.a`` is out of quorum.
The answer is ``a`` (that is, ``mon.a``). ``mon.a`` is out of quorum.

**How do we know, in this example, that mon.a is out of quorum?**

We know that ``mon.a`` is out of quorum because it has rank 0, and Monitors
with rank 0 are by definition out of quorum.
We know that ``mon.a`` is out of quorum because it has rank ``0``, and
Monitors with rank ``0`` are by definition out of quorum.

If we examine the ``quorum`` set, we can see that there are clearly two
monitors in the set: *1* and *2*. But these are not monitor names. They are
monitor ranks, as established in the current ``monmap``. The ``quorum`` set
does not include the monitor that has rank 0, and according to the ``monmap``
that monitor is ``mon.a``.
monitors in the set: ``1`` and ``2``. But these are not monitor names. They
are monitor ranks, as established in the current ``monmap``. The ``quorum``
set does not include the monitor that has rank ``0``, and according to the
``monmap`` that monitor is ``mon.a``.

**How are monitor ranks determined?**

Expand All @@ -192,7 +196,7 @@ a *peon*.
case, because ``127.0.0.1:6789`` (``mon.a``) is numerically less than the
other two ``IP:PORT`` combinations (which are ``127.0.0.1:6790`` for "Monitor
b" and ``127.0.0.1:6795`` for "Monitor c"), ``mon.a`` has the highest rank:
namely, rank 0.
namely, rank ``0``.


Most Common Monitor Issues
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