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+=====================================
+ Configuring Monitor/OSD Interaction
+=====================================
+
+.. index:: heartbeat
+
+After you have completed your initial Ceph configuration, you may deploy and run
+Ceph. When you execute a command such as ``ceph health`` or ``ceph -s``, the
+:term:`Ceph Monitor` reports on the current state of the :term:`Ceph Storage
+Cluster`. The Ceph Monitor knows about the Ceph Storage Cluster by requiring
+reports from each :term:`Ceph OSD Daemon`, and by receiving reports from Ceph
+OSD Daemons about the status of their neighboring Ceph OSD Daemons. If the Ceph
+Monitor doesn't receive reports, or if it receives reports of changes in the
+Ceph Storage Cluster, the Ceph Monitor updates the status of the :term:`Ceph
+Cluster Map`.
+
+Ceph provides reasonable default settings for Ceph Monitor/Ceph OSD Daemon
+interaction. However, you may override the defaults. The following sections
+describe how Ceph Monitors and Ceph OSD Daemons interact for the purposes of
+monitoring the Ceph Storage Cluster.
+
+.. index:: heartbeat interval
+
+OSDs Check Heartbeats
+=====================
+
+Each Ceph OSD Daemon checks the heartbeat of other Ceph OSD Daemons at random
+intervals less than every 6 seconds. If a neighboring Ceph OSD Daemon doesn't
+show a heartbeat within a 20 second grace period, the Ceph OSD Daemon may
+consider the neighboring Ceph OSD Daemon ``down`` and report it back to a Ceph
+Monitor, which will update the Ceph Cluster Map. You may change this grace
+period by adding an ``osd heartbeat grace`` setting under the ``[mon]``
+and ``[osd]`` or ``[global]`` section of your Ceph configuration file,
+or by setting the value at runtime.
+
+
+.. ditaa::
+ +---------+ +---------+
+ | OSD 1 | | OSD 2 |
+ +---------+ +---------+
+ | |
+ |----+ Heartbeat |
+ | | Interval |
+ |<---+ Exceeded |
+ | |
+ | Check |
+ | Heartbeat |
+ |------------------->|
+ | |
+ |<-------------------|
+ | Heart Beating |
+ | |
+ |----+ Heartbeat |
+ | | Interval |
+ |<---+ Exceeded |
+ | |
+ | Check |
+ | Heartbeat |
+ |------------------->|
+ | |
+ |----+ Grace |
+ | | Period |
+ |<---+ Exceeded |
+ | |
+ |----+ Mark |
+ | | OSD 2 |
+ |<---+ Down |
+
+
+.. index:: OSD down report
+
+OSDs Report Down OSDs
+=====================
+
+By default, two Ceph OSD Daemons from different hosts must report to the Ceph
+Monitors that another Ceph OSD Daemon is ``down`` before the Ceph Monitors
+acknowledge that the reported Ceph OSD Daemon is ``down``. But there is chance
+that all the OSDs reporting the failure are hosted in a rack with a bad switch
+which has trouble connecting to another OSD. To avoid this sort of false alarm,
+we consider the peers reporting a failure a proxy for a potential "subcluster"
+over the overall cluster that is similarly laggy. This is clearly not true in
+all cases, but will sometimes help us localize the grace correction to a subset
+of the system that is unhappy. ``mon osd reporter subtree level`` is used to
+group the peers into the "subcluster" by their common ancestor type in CRUSH
+map. By default, only two reports from different subtree are required to report
+another Ceph OSD Daemon ``down``. You can change the number of reporters from
+unique subtrees and the common ancestor type required to report a Ceph OSD
+Daemon ``down`` to a Ceph Monitor by adding an ``mon osd min down reporters``
+and ``mon osd reporter subtree level`` settings under the ``[mon]`` section of
+your Ceph configuration file, or by setting the value at runtime.
+
+
+.. ditaa::
+
+ +---------+ +---------+ +---------+
+ | OSD 1 | | OSD 2 | | Monitor |
+ +---------+ +---------+ +---------+
+ | | |
+ | OSD 3 Is Down | |
+ |---------------+--------------->|
+ | | |
+ | | |
+ | | OSD 3 Is Down |
+ | |--------------->|
+ | | |
+ | | |
+ | | |---------+ Mark
+ | | | | OSD 3
+ | | |<--------+ Down
+
+
+.. index:: peering failure
+
+OSDs Report Peering Failure
+===========================
+
+If a Ceph OSD Daemon cannot peer with any of the Ceph OSD Daemons defined in its
+Ceph configuration file (or the cluster map), it will ping a Ceph Monitor for
+the most recent copy of the cluster map every 30 seconds. You can change the
+Ceph Monitor heartbeat interval by adding an ``osd mon heartbeat interval``
+setting under the ``[osd]`` section of your Ceph configuration file, or by
+setting the value at runtime.
+
+.. ditaa::
+
+ +---------+ +---------+ +-------+ +---------+
+ | OSD 1 | | OSD 2 | | OSD 3 | | Monitor |
+ +---------+ +---------+ +-------+ +---------+
+ | | | |
+ | Request To | | |
+ | Peer | | |
+ |-------------->| | |
+ |<--------------| | |
+ | Peering | |
+ | | |
+ | Request To | |
+ | Peer | |
+ |----------------------------->| |
+ | |
+ |----+ OSD Monitor |
+ | | Heartbeat |
+ |<---+ Interval Exceeded |
+ | |
+ | Failed to Peer with OSD 3 |
+ |-------------------------------------------->|
+ |<--------------------------------------------|
+ | Receive New Cluster Map |
+
+
+.. index:: OSD status
+
+OSDs Report Their Status
+========================
+
+If an Ceph OSD Daemon doesn't report to a Ceph Monitor, the Ceph Monitor will
+consider the Ceph OSD Daemon ``down`` after the ``mon osd report timeout``
+elapses. A Ceph OSD Daemon sends a report to a Ceph Monitor when a reportable
+event such as a failure, a change in placement group stats, a change in
+``up_thru`` or when it boots within 5 seconds. You can change the Ceph OSD
+Daemon minimum report interval by adding an ``osd mon report interval``
+setting under the ``[osd]`` section of your Ceph configuration file, or by
+setting the value at runtime. A Ceph OSD Daemon sends a report to a Ceph
+Monitor every 120 seconds irrespective of whether any notable changes occur.
+You can change the Ceph Monitor report interval by adding an ``osd mon report
+interval max`` setting under the ``[osd]`` section of your Ceph configuration
+file, or by setting the value at runtime.
+
+
+.. ditaa::
+
+ +---------+ +---------+
+ | OSD 1 | | Monitor |
+ +---------+ +---------+
+ | |
+ |----+ Report Min |
+ | | Interval |
+ |<---+ Exceeded |
+ | |
+ |----+ Reportable |
+ | | Event |
+ |<---+ Occurs |
+ | |
+ | Report To |
+ | Monitor |
+ |------------------->|
+ | |
+ |----+ Report Max |
+ | | Interval |
+ |<---+ Exceeded |
+ | |
+ | Report To |
+ | Monitor |
+ |------------------->|
+ | |
+ |----+ Monitor |
+ | | Fails |
+ |<---+ |
+ +----+ Monitor OSD
+ | | Report Timeout
+ |<---+ Exceeded
+ |
+ +----+ Mark
+ | | OSD 1
+ |<---+ Down
+
+
+
+
+Configuration Settings
+======================
+
+When modifying heartbeat settings, you should include them in the ``[global]``
+section of your configuration file.
+
+.. index:: monitor heartbeat
+
+Monitor Settings
+----------------
+
+``mon osd min up ratio``
+
+:Description: The minimum ratio of ``up`` Ceph OSD Daemons before Ceph will
+ mark Ceph OSD Daemons ``down``.
+
+:Type: Double
+:Default: ``.3``
+
+
+``mon osd min in ratio``
+
+:Description: The minimum ratio of ``in`` Ceph OSD Daemons before Ceph will
+ mark Ceph OSD Daemons ``out``.
+
+:Type: Double
+:Default: ``.75``
+
+
+``mon osd laggy halflife``
+
+:Description: The number of seconds laggy estimates will decay.
+:Type: Integer
+:Default: ``60*60``
+
+
+``mon osd laggy weight``
+
+:Description: The weight for new samples in laggy estimation decay.
+:Type: Double
+:Default: ``0.3``
+
+
+
+``mon osd laggy max interval``
+
+:Description: Maximum value of ``laggy_interval`` in laggy estimations (in seconds).
+ Monitor uses an adaptive approach to evaluate the ``laggy_interval`` of
+ a certain OSD. This value will be used to calculate the grace time for
+ that OSD.
+:Type: Integer
+:Default: 300
+
+``mon osd adjust heartbeat grace``
+
+:Description: If set to ``true``, Ceph will scale based on laggy estimations.
+:Type: Boolean
+:Default: ``true``
+
+
+``mon osd adjust down out interval``
+
+:Description: If set to ``true``, Ceph will scaled based on laggy estimations.
+:Type: Boolean
+:Default: ``true``
+
+
+``mon osd auto mark in``
+
+:Description: Ceph will mark any booting Ceph OSD Daemons as ``in``
+ the Ceph Storage Cluster.
+
+:Type: Boolean
+:Default: ``false``
+
+
+``mon osd auto mark auto out in``
+
+:Description: Ceph will mark booting Ceph OSD Daemons auto marked ``out``
+ of the Ceph Storage Cluster as ``in`` the cluster.
+
+:Type: Boolean
+:Default: ``true``
+
+
+``mon osd auto mark new in``
+
+:Description: Ceph will mark booting new Ceph OSD Daemons as ``in`` the
+ Ceph Storage Cluster.
+
+:Type: Boolean
+:Default: ``true``
+
+
+``mon osd down out interval``
+
+:Description: The number of seconds Ceph waits before marking a Ceph OSD Daemon
+ ``down`` and ``out`` if it doesn't respond.
+
+:Type: 32-bit Integer
+:Default: ``600``
+
+
+``mon osd down out subtree limit``
+
+:Description: The smallest :term:`CRUSH` unit type that Ceph will **not**
+ automatically mark out. For instance, if set to ``host`` and if
+ all OSDs of a host are down, Ceph will not automatically mark out
+ these OSDs.
+
+:Type: String
+:Default: ``rack``
+
+
+``mon osd report timeout``
+
+:Description: The grace period in seconds before declaring
+ unresponsive Ceph OSD Daemons ``down``.
+
+:Type: 32-bit Integer
+:Default: ``900``
+
+``mon osd min down reporters``
+
+:Description: The minimum number of Ceph OSD Daemons required to report a
+ ``down`` Ceph OSD Daemon.
+
+:Type: 32-bit Integer
+:Default: ``2``
+
+
+``mon osd reporter subtree level``
+
+:Description: In which level of parent bucket the reporters are counted. The OSDs
+ send failure reports to monitor if they find its peer is not responsive.
+ And monitor mark the reported OSD out and then down after a grace period.
+:Type: String
+:Default: ``host``
+
+
+.. index:: OSD hearbeat
+
+OSD Settings
+------------
+
+``osd heartbeat address``
+
+:Description: An Ceph OSD Daemon's network address for heartbeats.
+:Type: Address
+:Default: The host address.
+
+
+``osd heartbeat interval``
+
+:Description: How often an Ceph OSD Daemon pings its peers (in seconds).
+:Type: 32-bit Integer
+:Default: ``6``
+
+
+``osd heartbeat grace``
+
+:Description: The elapsed time when a Ceph OSD Daemon hasn't shown a heartbeat
+ that the Ceph Storage Cluster considers it ``down``.
+ This setting has to be set in both the [mon] and [osd] or [global]
+ section so that it is read by both the MON and OSD daemons.
+:Type: 32-bit Integer
+:Default: ``20``
+
+
+``osd mon heartbeat interval``
+
+:Description: How often the Ceph OSD Daemon pings a Ceph Monitor if it has no
+ Ceph OSD Daemon peers.
+
+:Type: 32-bit Integer
+:Default: ``30``
+
+
+``osd mon heartbeat stat stale``
+
+:Description: Stop reporting on heartbeat ping times which haven't been updated for
+ this many seconds. Set to zero to disable this action.
+
+:Type: 32-bit Integer
+:Default: ``3600``
+
+
+``osd mon report interval``
+
+:Description: The number of seconds a Ceph OSD Daemon may wait
+ from startup or another reportable event before reporting
+ to a Ceph Monitor.
+
+:Type: 32-bit Integer
+:Default: ``5``
+
+
+``osd mon ack timeout``
+
+:Description: The number of seconds to wait for a Ceph Monitor to acknowledge a
+ request for statistics.
+
+:Type: 32-bit Integer
+:Default: ``30``
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