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| -rw-r--r-- | doc/dev/ceph-volume/systemd.rst | 37 |
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diff --git a/doc/dev/ceph-volume/systemd.rst b/doc/dev/ceph-volume/systemd.rst new file mode 100644 index 000000000..8553430ee --- /dev/null +++ b/doc/dev/ceph-volume/systemd.rst @@ -0,0 +1,37 @@ +.. _ceph-volume-systemd-api: + +systemd +======= +The workflow to *"activate"* an OSD is by relying on systemd unit files and its +ability to persist information as a suffix to the instance name. + +``ceph-volume`` exposes the following convention for unit files:: + + ceph-volume@<sub command>-<extra metadata> + +For example, this is how enabling an OSD could look like for the +:ref:`ceph-volume-lvm` sub command:: + + systemctl enable ceph-volume@lvm-0-8715BEB4-15C5-49DE-BA6F-401086EC7B41 + + +These 3 pieces of persisted information are needed by the sub-command so that +it understands what OSD it needs to activate. + +Since ``lvm`` is not the only subcommand that will be supported, this +is how it will allow other device types to be defined. + +At some point for example, for plain disks, it could be:: + + systemctl enable ceph-volume@disk-0-8715BEB4-15C5-49DE-BA6F-401086EC7B41 + +At startup, the systemd unit will execute a helper script that will parse the +suffix and will end up calling ``ceph-volume`` back. Using the previous +example for lvm, that call will look like:: + + ceph-volume lvm activate 0 8715BEB4-15C5-49DE-BA6F-401086EC7B41 + + +.. warning:: These workflows are not meant to be public, but are documented so that + it is clear what the tool is doing behind the scenes. Do not alter + any of these values. |