Once prepare is completed, and all the various steps that entails are done, the volume is ready to get “activated”.
This activation process enables a systemd unit that persists the OSD ID and its
UUID (also called
fsid in Ceph CLI tools), so that at boot time it can
understand what OSD is enabled and needs to be mounted.
The execution of this call is fully idempotent, and there is no side-effects when running multiple times
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¶
It is possible to activate all existing OSDs at once by using the
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).
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
--dmcrypt on the command line again (that flag is not available for
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.
systemctl enable ceph-volume@lvm-$id-$uuid
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
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>/)
# ensure that all required devices are ready for that OSD. In the case of
a journal (when
--filestore is selected) the device will be queried (with
blkid for partitions, and lvm for logical volumes) to ensure that the
correct device is being linked. The symbolic link will always be re-done to
ensure that the correct device is linked.
# start the
ceph-osd@0 systemd unit
The system infers the objectstore type (filestore or bluestore) by inspecting the LVM tags applied to the OSD devices
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 tooling 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:
enable the system unit with matching id and uuid
tmpfsmount at the OSD directory in
Recreate all the files needed with
ceph-bluestore-tool prime-osd-dirby pointing it to the OSD
the systemd unit will ensure all devices are ready and linked
ceph-osdsystemd unit will get started
And for filestore: