Configuring Monitor/OSD Interaction

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 Ceph Monitor reports on the current state of the Ceph Storage Cluster. The Ceph Monitor knows about the Ceph Storage Cluster by requiring reports from each 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 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.

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.

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.

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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.

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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.

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Configuration Settings

When modifying heartbeat settings, you should include them in the [global] section of your configuration file.

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 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 monitors if they find a peer that is not responsive. Monitors mark the reported OSD out and then down after a grace period.

Type

String

Default

host

OSD Settings

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 must be set in both the [mon] and [osd] or [global] sections so that it is read by both monitor 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