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50 lines
2.0 KiB
ReStructuredText
50 lines
2.0 KiB
ReStructuredText
.. _ceph-volume-systemd:
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systemd
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=======
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As part of the activation process (either with :ref:`ceph-volume-lvm-activate`
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or :ref:`ceph-volume-simple-activate`), systemd units will get enabled that
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will use the OSD id and uuid as part of their name. These units will be run
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when the system boots, and will proceed to activate their corresponding
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volumes via their sub-command implementation.
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The API for activation is a bit loose, it only requires two parts: the
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subcommand to use and any extra meta information separated by a dash. This
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convention makes the units look like::
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ceph-volume@{command}-{extra metadata}
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The *extra metadata* can be anything needed that the subcommand implementing
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the processing might need. In the case of :ref:`ceph-volume-lvm` and
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:ref:`ceph-volume-simple`, both look to consume the :term:`OSD id` and :term:`OSD uuid`,
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but this is not a hard requirement, it is just how the sub-commands are
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implemented.
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Both the command and extra metadata gets persisted by systemd as part of the
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*"instance name"* of the unit. For example an OSD with an ID of 0, for the
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``lvm`` sub-command would look like::
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systemctl enable ceph-volume@lvm-0-0A3E1ED2-DA8A-4F0E-AA95-61DEC71768D6
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The enabled unit is a :term:`systemd oneshot` service, meant to start at boot
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after the local filesystem is ready to be used.
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Failure and Retries
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-------------------
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It is common to have failures when a system is coming up online. The devices
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are sometimes not fully available and this unpredictable behavior may cause an
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OSD to not be ready to be used.
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There are two configurable environment variables used to set the retry
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behavior:
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* ``CEPH_VOLUME_SYSTEMD_TRIES``: Defaults to 30
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* ``CEPH_VOLUME_SYSTEMD_INTERVAL``: Defaults to 5
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The *"tries"* is a number that sets the maximum amount of times the unit will
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attempt to activate an OSD before giving up.
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The *"interval"* is a value in seconds that determines the waiting time before
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initiating another try at activating the OSD.
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