After prepare has completed its run, the volume can be activated.

Activating the volume involves enabling a systemd unit that persists the OSD ID and its UUID (which is also called the fsid in the Ceph CLI tools). After this information has been persisted, the cluster can determine which OSD is enabled and must be mounted.


The execution of this call is fully idempotent. This means that the call can be executed multiple times without changing the result of its first successful execution.

For information about OSDs deployed by cephadm, refer to Activate existing OSDs.

New OSDs

To activate newly prepared OSDs both the OSD id and OSD uuid need to be supplied. For example:

ceph-volume lvm activate --bluestore 0 0263644D-0BF1-4D6D-BC34-28BD98AE3BC8


The UUID is stored in the fsid file in the OSD path, which is generated when prepare is used.

Activating all OSDs


For OSDs deployed by cephadm, please refer to Activate existing OSDs instead.

It is possible to activate all existing OSDs at once by using the --all flag. For example:

ceph-volume lvm activate --all

This call will inspect all the OSDs created by ceph-volume that are inactive and will activate them one by one. If any of the OSDs are already running, it will report them in the command output and skip them, making it safe to rerun (idempotent).

requiring uuids

The OSD uuid is being required as an extra step to ensure that the right OSD is being activated. It is entirely possible that a previous OSD with the same id exists and would end up activating the incorrect one.


If the OSD was prepared with dmcrypt by ceph-volume, there is no need to specify --dmcrypt on the command line again (that flag is not available for the activate subcommand). An encrypted OSD will be automatically detected.


With OSDs previously created by ceph-volume, a discovery process is performed using LVM tags to enable the systemd units.

The systemd unit will capture the OSD id and OSD uuid and persist it. Internally, the activation will enable it like:

systemctl enable ceph-volume@lvm-$id-$uuid

For example:

systemctl enable ceph-volume@lvm-0-8715BEB4-15C5-49DE-BA6F-401086EC7B41

Would start the discovery process for the OSD with an id of 0 and a UUID of 8715BEB4-15C5-49DE-BA6F-401086EC7B41.


for more details on the systemd workflow see systemd

The systemd unit will look for the matching OSD device, and by looking at its LVM tags will proceed to:

#. Mount the device in the corresponding location (by convention this is /var/lib/ceph/osd/<cluster name>-<osd id>/)

  1. Ensure that all required devices are ready for that OSD.

  2. Start the ceph-osd@0 systemd unit


The system infers the objectstore type by inspecting the LVM tags applied to the OSD devices

Existing OSDs

For existing OSDs that have been deployed with ceph-disk, they need to be scanned and activated using the simple sub-command. If a different tool was used then the only way to port them over to the new mechanism is to prepare them again (losing data). See Existing OSDs for details on how to proceed.


To recap the activate process for bluestore:

  1. Require both OSD id and OSD uuid

  2. Enable the system unit with matching id and uuid

  3. Create the tmpfs mount at the OSD directory in /var/lib/ceph/osd/$cluster-$id/

  4. Recreate all the files needed with ceph-bluestore-tool prime-osd-dir by pointing it to the OSD block device.

  5. The systemd unit will ensure all devices are ready and linked

  6. The matching ceph-osd systemd unit will get started