Juju Charm - Ceph OSD
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Ceph is a unified, distributed storage system designed for excellent performance, reliability, and scalability.

The ceph-osd charm deploys the Ceph object storage daemon (OSD) and manages its volumes. It is used in conjunction with the ceph-mon charm. Together, these charms can scale out the amount of storage available in a Ceph cluster.



This section covers common and/or important configuration options. See file config.yaml for the full list of options, along with their descriptions and default values. A YAML file (e.g. ceph-osd.yaml) is often used to store configuration options. See the Juju documentation for details on configuring applications.


The bluestore option specifies whether the BlueStore storage backend is used for all OSD devices. The feature is enabled by default (value ‘True’). If set to ‘True’, this option overrides the osd-format option as BlueStore does not use a traditional filesystem.

Important: This option has no effect unless Ceph Luminous (or greater) is in use.


The customize-failure-domain option determines how a Ceph CRUSH map is configured.

A value of ‘false’ (the default) will lead to a map that will replicate data across hosts (implemented as Ceph bucket type ‘host’). With a value of ‘true’ all MAAS-defined zones will be used to generate a map that will replicate data across Ceph availability zones (implemented as bucket type ‘rack’).

This option is also supported by the ceph-mon charm. Its value must be the same for both charms.


The osd-devices option lists what block devices can be used for OSDs across the cluster. See section ‘Storage devices’ for an elaboration on this fundamental topic.


The osd-format option specifies what filesystem to use for all OSD devices (‘xfs’ or ‘ext4’). The default value is ‘xfs’. This option only applies when Ceph Luminous (or greater) is in use and option bluestore is set to ‘False’.


The source option states the software sources. A common value is an OpenStack UCA release (e.g. ‘cloud:xenial-queens’ or ‘cloud:bionic-ussuri’). See Ceph and the UCA. The underlying host’s existing apt sources will be used if this option is not specified (this behaviour can be explicitly chosen by using the value of ‘distro’).

Storage devices

A storage device is destined as an OSD (Object Storage Device). There can be multiple OSDs per storage node (ceph-osd unit).

The list of all possible storage devices for the cluster is defined by the osd-devices option (default value is ‘/dev/vdb’). The below examples can be used in the ceph-osd.yaml configuration file.

Block devices (regular),

    osd-devices: /dev/vdb /dev/vdc /dev/vdd

Each regular block device must be an absolute path to a device node.

Block devices (Juju storage),

    osd-devices: cinder,20G

See the Juju documentation for guidance on implementing Juju storage.

Directory-backed OSDs,

    osd-devices: /var/tmp/osd-1

Note: OSD directories can no longer be created starting with Ceph Nautilus. Existing OSD directories will continue to function after an upgrade to Nautilus.

The list defined by option osd-devices may affect newly added ceph-osd units as well as existing units (the option may be modified after units have been added). The charm will attempt to activate as Ceph storage any listed device that is visible by the unit’s underlying machine. To prevent the activation of volumes on existing units the blacklist-add-disk action may be used.

The configuration option is modified in the usual way. For instance, to have it consist solely of devices ‘/dev/sdb’ and ‘/dev/sdc’:

juju config ceph-osd osd-devices='/dev/sdb /dev/sdc'

The charm will go into a blocked state (visible in juju status output) if it detects pre-existing data on a device. In this case the operator can either instruct the charm to ignore the disk (action blacklist-add-disk) or to have it purge all data on the disk (action zap-disk).

Important: The recommended minimum number of OSDs in the cluster is three and this is what the ceph-mon charm expects (the cluster will not form with a lesser number). See option expected-osd-count in the ceph-mon charm to overcome this but beware that going below three is not a supported configuration.


A cloud with three MON nodes is a typical design whereas three OSDs are considered the minimum. For example, to deploy a Ceph cluster consisting of three OSDs (one per ceph-osd unit) and three MONs:

juju deploy -n 3 --config ceph-osd.yaml ceph-osd
juju deploy -n 3 --to lxd:0,lxd:1,lxd:2 ceph-mon
juju add-relation ceph-osd:mon ceph-mon:osd

Here, a containerised MON is running alongside each storage node. We’ve assumed that the machines spawned in the first command are assigned IDs of 0, 1, and 2.

Note: Refer to the Install OpenStack page in the OpenStack Charms Deployment Guide for instructions on installing the ceph-osd application for use with OpenStack.

For each ceph-osd unit, the ceph-osd charm will scan for all the devices configured via the osd-devices option and attempt to assign to it all of the ones it finds. The cluster’s initial pool of available storage is the “sum” of all these assigned devices.

Network spaces

This charm supports the use of Juju network spaces (Juju v.2.0). This feature optionally allows specific types of the application’s network traffic to be bound to subnets that the underlying hardware is connected to.

Note: Spaces must be configured in the backing cloud prior to deployment.

The ceph-osd charm exposes the following Ceph traffic types (bindings):

  • ‘public’ (front-side)
  • ‘cluster’ (back-side)

For example, providing that spaces ‘data-space’ and ‘cluster-space’ exist, the deploy command above could look like this:

juju deploy --config ceph-osd.yaml -n 3 ceph-osd \
   --bind "public=data-space cluster=cluster-space"

Alternatively, configuration can be provided as part of a bundle:

      charm: cs:ceph-osd
      num_units: 1
        public: data-space
        cluster: cluster-space

Refer to the Ceph Network Reference to learn about the implications of segregating Ceph network traffic.

Note: Existing ceph-osd units configured with the ceph-public-network or ceph-cluster-network options will continue to honour them. Furthermore, these options override any space bindings, if set.

AppArmor profiles

Although AppArmor is not enabled for Ceph by default, an AppArmor profile can be generated by the charm by assigning a value of ‘complain’, ‘enforce’, or ‘disable’ (the default) to option aa-profile-mode.

Caution: Enabling an AppArmor profile is disruptive to a running Ceph cluster as all ceph-osd processes must be restarted.

The new profile has a narrow supported use case, and it should always be verified in pre-production against the specific configurations and topologies intended for production.

The profiles generated by the charm should not be used in the following scenarios:

  • On any version of Ubuntu older than 16.04
  • On any version of Ceph older than Luminous
  • When OSD journal devices are in use
  • When Ceph BlueStore is enabled

Block device encryption

The ceph-osd charm supports encryption for OSD volumes that are backed by block devices. To use Ceph’s native key management framework, available since Ceph Jewel, set option osd-encrypt for the ceph-osd charm:

        osd-encrypt: True

Here, dm-crypt keys are stored in the MON sub-cluster.

Alternatively, since Ceph Luminous, encryption keys can be stored in Vault, which is deployed and initialised via the vault charm. Set options osd-encrypt and osd-encrypt-keymanager for the ceph-osd charm:

        osd-encrypt: True
        osd-encrypt-keymanager: vault

Important: Post deployment configuration will only affect block devices associated with new ceph-osd units.


This section covers Juju actions supported by the charm. Actions allow specific operations to be performed on a per-unit basis. To display action descriptions run juju actions ceph-osd. If the charm is not deployed then see file actions.yaml.

  • add-disk
  • blacklist-add-disk
  • blacklist-remove-disk
  • list-disks
  • osd-in
  • osd-out
  • security-checklist
  • zap-disk

Working with OSDs

Set OSDs to ‘out’

Use the osd-out action to set all OSD volumes on a unit to ‘out’.

Warning: This action has the potential of impacting your cluster significantly. The Ceph documentation on this topic is considered essential reading.

The osd-out action sets all OSDs on the unit as ‘out’. Unless the cluster itself is set to ‘noout’ this action will cause Ceph to rebalance data by migrating PGs out of the unit’s OSDs and onto OSDs available on other units. The impact is twofold:

  1. The available space on the remaining OSDs is reduced. Not only is there less space for future workloads but there is a danger of exceeding the cluster’s storage capacity.
  2. The traffic and CPU load on the cluster is increased.

Note: It has been reported that setting OSDs as ‘out’ may cause some PGs to get stuck in the ‘active+remapped’ state. This is an upstream issue.

The ceph-mon charm has an action called set-noout that sets ‘noout’ for the cluster.

It may be perfectly fine to have data rebalanced. The decisive factor is whether the OSDs are being paused temporarily (e.g. the underlying machine is scheduled for maintenance) or whether they are being removed from the cluster completely (e.g. the storage hardware is reaching EOL).


juju run-action --wait ceph-osd/4 osd-out

Set OSDs to ‘in’

Use the osd-in action to set all OSD volumes on a unit to ‘in’.

The osd-in action is reciprocal to the osd-out action. The OSDs are set to ‘in’. It is typically used when the osd-out action was used in conjunction with the cluster ‘noout’ flag.


juju run-action --wait ceph-osd/4 osd-in

Working with disks

List disks

Use the list-disks action to list disks known to a unit.

The action lists the unit’s block devices by categorising them in three ways:

  • disks: visible (known by udev), unused (not mounted), and not designated as an OSD journal (via the osd-journal configuration option)

  • blacklist: like disks but blacklisted (see action blacklist-add-disk)

  • non-pristine: like disks but not eligible for use due to the presence of existing data


juju run-action --wait ceph-osd/4 list-disks

Add a disk

Use the add-disk action to add a disk to a unit.

A ceph-osd unit is automatically assigned OSD volumes based on the current value of the osd-devices application option. The add-disk action allows the operator to manually add OSD volumes (for disks that are not listed by osd-devices) to an existing unit.


  • osd-devices (required)
    A space-separated list of devices to format and initialise as OSD volumes.
  • bucket
    The name of a Ceph bucket to add these devices to.


juju run-action --wait ceph-osd/4 add-disk osd-devices=/dev/vde

Blacklist a disk

Use the blacklist-add-disk action to add a disk to a unit’s blacklist.

The action allows the operator to add disks (that are visible to the unit’s underlying machine) to the unit’s blacklist. A blacklisted device will not be initialised as an OSD volume when the value of the osd-devices application option changes. This action does not prevent a device from being activated via the add-disk action.

Use the list-disks action to list the unit’s blacklist entries.

Important: This action and blacklist do not have any effect on current OSD volumes.


  • osd-devices (required)
    A space-separated list of devices to add to a unit’s blacklist.


juju run-action --wait ceph-osd/0 \
   blacklist-add-disk osd-devices='/dev/vda /dev/vdf'

Un-blacklist a disk

Use the blacklist-remove-disk action to remove a disk from a unit’s blacklist.


  • osd-devices (required)
    A space-separated list of devices to remove from a unit’s blacklist.

Each device should have an existing entry in the unit’s blacklist. Use the list-disks action to list the unit’s blacklist entries.


juju run-action --wait ceph-osd/1 \
   blacklist-remove-disk osd-devices=/dev/vdb

Zap a disk

Use the zap-disk action to purge a disk of all data.

In order to prevent unintentional data loss, the charm will not use a disk that has existing data already on it. To forcibly make a disk available, the zap-disk action can be used. Due to the destructive nature of this action the i-really-mean-it option must be passed. This action is normally followed by the add-disk action.


  • devices (required)
    A space-separated list of devices to be recycled.
  • i-really-mean-it (required)
    An option that acts as a confirmation for performing the action.


juju run-action --wait ceph-osd/3 zap-disk i-really-mean-it=true devices=/dev/vdc

Note: The zap-disk action cannot be run on a mounted device, an active Bluestore device, or an encrypted device.


Please report bugs on Launchpad.

For general charm questions refer to the OpenStack Charm Guide.