======================
 Monitoring a Cluster
======================

Once you have a running cluster, you may use the ``ceph`` tool to monitor your
cluster. Monitoring a cluster typically involves checking OSD status, monitor 
status, placement group status and metadata server status.

Using the command line
======================

Interactive mode
----------------

To run the ``ceph`` tool in interactive mode, type ``ceph`` at the command line
with no arguments.  For example:: 

	ceph
	ceph> health
	ceph> status
	ceph> quorum_status
	ceph> mon_status

Non-default paths
-----------------

If you specified non-default locations for your configuration or keyring,
you may specify their locations::

   ceph -c /path/to/conf -k /path/to/keyring health

Checking a Cluster's Status
===========================

After you start your cluster, and before you start reading and/or
writing data, check your cluster's status first.

To check a cluster's status, execute the following:: 

	ceph status
	
Or:: 

	ceph -s

In interactive mode, type ``status`` and press **Enter**. ::

	ceph> status

Ceph will print the cluster status. For example, a tiny Ceph demonstration
cluster with one of each service may print the following:

::

  cluster:
    id:     477e46f1-ae41-4e43-9c8f-72c918ab0a20
    health: HEALTH_OK
   
  services:
    mon: 1 daemons, quorum a
    mgr: x(active)
    mds: 1/1/1 up {0=a=up:active}
    osd: 1 osds: 1 up, 1 in
  
  data:
    pools:   2 pools, 16 pgs
    objects: 21 objects, 2246 bytes
    usage:   546 GB used, 384 GB / 931 GB avail
    pgs:     16 active+clean


.. topic:: How Ceph Calculates Data Usage

   The ``usage`` value reflects the *actual* amount of raw storage used. The 
   ``xxx GB / xxx GB`` value means the amount available (the lesser number)
   of the overall storage capacity of the cluster. The notional number reflects 
   the size of the stored data before it is replicated, cloned or snapshotted.
   Therefore, the amount of data actually stored typically exceeds the notional
   amount stored, because Ceph creates replicas of the data and may also use 
   storage capacity for cloning and snapshotting.


Watching a Cluster
==================

In addition to local logging by each daemon, Ceph clusters maintain
a *cluster log* that records high level events about the whole system.
This is logged to disk on monitor servers (as ``/var/log/ceph/ceph.log`` by
default), but can also be monitored via the command line.

To follow the cluster log, use the following command

:: 

	ceph -w

Ceph will print the status of the system, followed by each log message as it
is emitted.  For example:

:: 

  cluster:
    id:     477e46f1-ae41-4e43-9c8f-72c918ab0a20
    health: HEALTH_OK
  
  services:
    mon: 1 daemons, quorum a
    mgr: x(active)
    mds: 1/1/1 up {0=a=up:active}
    osd: 1 osds: 1 up, 1 in
  
  data:
    pools:   2 pools, 16 pgs
    objects: 21 objects, 2246 bytes
    usage:   546 GB used, 384 GB / 931 GB avail
    pgs:     16 active+clean
  
  
  2017-07-24 08:15:11.329298 mon.a mon.0 172.21.9.34:6789/0 23 : cluster [INF] osd.0 172.21.9.34:6806/20527 boot
  2017-07-24 08:15:14.258143 mon.a mon.0 172.21.9.34:6789/0 39 : cluster [INF] Activating manager daemon x
  2017-07-24 08:15:15.446025 mon.a mon.0 172.21.9.34:6789/0 47 : cluster [INF] Manager daemon x is now available


In addition to using ``ceph -w`` to print log lines as they are emitted,
use ``ceph log last [n]`` to see the most recent ``n`` lines from the cluster
log.

Monitoring Health Checks
========================

Ceph continously runs various *health checks* against its own status.  When
a health check fails, this is reflected in the output of ``ceph status`` (or
``ceph health``).  In addition, messages are sent to the cluster log to
indicate when a check fails, and when the cluster recovers.

For example, when an OSD goes down, the ``health`` section of the status
output may be updated as follows:

::

    health: HEALTH_WARN
            1 osds down
            Degraded data redundancy: 21/63 objects degraded (33.333%), 16 pgs unclean, 16 pgs degraded

At this time, cluster log messages are also emitted to record the failure of the 
health checks:

::

    2017-07-25 10:08:58.265945 mon.a mon.0 172.21.9.34:6789/0 91 : cluster [WRN] Health check failed: 1 osds down (OSD_DOWN)
    2017-07-25 10:09:01.302624 mon.a mon.0 172.21.9.34:6789/0 94 : cluster [WRN] Health check failed: Degraded data redundancy: 21/63 objects degraded (33.333%), 16 pgs unclean, 16 pgs degraded (PG_DEGRADED)

When the OSD comes back online, the cluster log records the cluster's return
to a health state:

::

    2017-07-25 10:11:11.526841 mon.a mon.0 172.21.9.34:6789/0 109 : cluster [WRN] Health check update: Degraded data redundancy: 2 pgs unclean, 2 pgs degraded, 2 pgs undersized (PG_DEGRADED)
    2017-07-25 10:11:13.535493 mon.a mon.0 172.21.9.34:6789/0 110 : cluster [INF] Health check cleared: PG_DEGRADED (was: Degraded data redundancy: 2 pgs unclean, 2 pgs degraded, 2 pgs undersized)
    2017-07-25 10:11:13.535577 mon.a mon.0 172.21.9.34:6789/0 111 : cluster [INF] Cluster is now healthy


Detecting configuration issues
==============================

In addition to the health checks that Ceph continuously runs on its
own status, there are some configuration issues that may only be detected
by an external tool.

Use the `ceph-medic`_ tool to run these additional checks on your Ceph
cluster's configuration.

Checking a Cluster's Usage Stats
================================

To check a cluster's data usage and data distribution among pools, you can
use the ``df`` option. It is similar to Linux ``df``. Execute 
the following::

	ceph df

The **GLOBAL** section of the output provides an overview of the amount of 
storage your cluster uses for your data.

- **SIZE:** The overall storage capacity of the cluster.
- **AVAIL:** The amount of free space available in the cluster.
- **RAW USED:** The amount of raw storage used.
- **% RAW USED:** The percentage of raw storage used. Use this number in 
  conjunction with the ``full ratio`` and ``near full ratio`` to ensure that 
  you are not reaching your cluster's capacity. See `Storage Capacity`_ for 
  additional details.

The **POOLS** section of the output provides a list of pools and the notional 
usage of each pool. The output from this section **DOES NOT** reflect replicas,
clones or snapshots. For example, if you store an object with 1MB of data, the 
notional usage will be 1MB, but the actual usage may be 2MB or more depending 
on the number of replicas, clones and snapshots.

- **NAME:** The name of the pool.
- **ID:** The pool ID.
- **USED:** The notional amount of data stored in kilobytes, unless the number 
  appends **M** for megabytes or **G** for gigabytes.
- **%USED:** The notional percentage of storage used per pool.
- **MAX AVAIL:** An estimate of the notional amount of data that can be written
  to this pool.
- **Objects:** The notional number of objects stored per pool.

.. note:: The numbers in the **POOLS** section are notional. They are not 
   inclusive of the number of replicas, shapshots or clones. As a result, 
   the sum of the **USED** and **%USED** amounts will not add up to the 
   **RAW USED** and **%RAW USED** amounts in the **GLOBAL** section of the 
   output.

.. note:: The **MAX AVAIL** value is a complicated function of the
   replication or erasure code used, the CRUSH rule that maps storage
   to devices, the utilization of those devices, and the configured
   mon_osd_full_ratio.



Checking OSD Status
===================

You can check OSDs to ensure they are ``up`` and ``in`` by executing:: 

	ceph osd stat
	
Or:: 

	ceph osd dump
	
You can also check view OSDs according to their position in the CRUSH map. :: 

	ceph osd tree

Ceph will print out a CRUSH tree with a host, its OSDs, whether they are up
and their weight. ::  

	# id	weight	type name	up/down	reweight
	-1	3	pool default
	-3	3		rack mainrack
	-2	3			host osd-host
	0	1				osd.0	up	1	
	1	1				osd.1	up	1	
	2	1				osd.2	up	1

For a detailed discussion, refer to `Monitoring OSDs and Placement Groups`_.

Checking Monitor Status
=======================

If your cluster has multiple monitors (likely), you should check the monitor
quorum status after you start the cluster before reading and/or writing data. A
quorum must be present when multiple monitors are running. You should also check
monitor status periodically to ensure that they are running.

To see display the monitor map, execute the following::

	ceph mon stat
	
Or:: 

	ceph mon dump
	
To check the quorum status for the monitor cluster, execute the following:: 
	
	ceph quorum_status

Ceph will return the quorum status. For example, a Ceph  cluster consisting of
three monitors may return the following:

.. code-block:: javascript

	{ "election_epoch": 10,
	  "quorum": [
	        0,
	        1,
	        2],
	  "monmap": { "epoch": 1,
	      "fsid": "444b489c-4f16-4b75-83f0-cb8097468898",
	      "modified": "2011-12-12 13:28:27.505520",
	      "created": "2011-12-12 13:28:27.505520",
	      "mons": [
	            { "rank": 0,
	              "name": "a",
	              "addr": "127.0.0.1:6789\/0"},
	            { "rank": 1,
	              "name": "b",
	              "addr": "127.0.0.1:6790\/0"},
	            { "rank": 2,
	              "name": "c",
	              "addr": "127.0.0.1:6791\/0"}
	           ]
	    }
	}

Checking MDS Status
===================

Metadata servers provide metadata services for  Ceph FS. Metadata servers have
two sets of states: ``up | down`` and ``active | inactive``. To ensure your
metadata servers are ``up`` and ``active``,  execute the following:: 

	ceph mds stat
	
To display details of the metadata cluster, execute the following:: 

	ceph fs dump


Checking Placement Group States
===============================

Placement groups map objects to OSDs. When you monitor your
placement groups,  you will want them to be ``active`` and ``clean``. 
For a detailed discussion, refer to `Monitoring OSDs and Placement Groups`_.

.. _Monitoring OSDs and Placement Groups: ../monitoring-osd-pg


Using the Admin Socket
======================

The Ceph admin socket allows you to query a daemon via a socket interface. 
By default, Ceph sockets reside under ``/var/run/ceph``. To access a daemon
via the admin socket, login to the host running the daemon and use the 
following command:: 

	ceph daemon {daemon-name}
	ceph daemon {path-to-socket-file}

For example, the following are equivalent::

    ceph daemon osd.0 foo
    ceph daemon /var/run/ceph/ceph-osd.0.asok foo

To view the available admin socket commands, execute the following command:: 

	ceph daemon {daemon-name} help

The admin socket command enables you to show and set your configuration at
runtime. See `Viewing a Configuration at Runtime`_ for details.

Additionally, you can set configuration values at runtime directly (i.e., the
admin socket bypasses the monitor, unlike ``ceph tell {daemon-type}.{id}
injectargs``, which relies on the monitor but doesn't require you to login
directly to the host in question ).

.. _Viewing a Configuration at Runtime: ../../configuration/ceph-conf#ceph-runtime-config
.. _Storage Capacity: ../../configuration/mon-config-ref#storage-capacity
.. _ceph-medic: http://docs.ceph.com/ceph-medic/master/
