.. _ceph-volume-lvm-prepare: ``prepare`` =========== This subcommand allows a :term:`filestore` setup (:term:`bluestore` support is planned) and currently consumes only logical volumes for both the data and journal. It will not create or modify the logical volumes except for adding extra metadata. .. note:: This is part of a two step process to deploy an OSD. If looking for a single-call way, please see :ref:`ceph-volume-lvm-create` To help identify volumes, the process of preparing a volume (or volumes) to work with Ceph, the tool will assign a few pieces of metadata information using :term:`LVM tags`. :term:`LVM tags` makes volumes easy to discover later, and help identify them as part of a Ceph system, and what role they have (journal, filestore, bluestore, etc...) Although initially :term:`filestore` is supported (and supported by default) the back end can be specified with: * :ref:`--filestore ` * ``--bluestore`` .. when available, this will need to be updated to: .. * :ref:`--bluestore ` .. _ceph-volume-lvm-prepare_filestore: ``filestore`` ------------- This is the default OSD backend and allows preparation of logical volumes for a :term:`filestore` OSD. The process is *very* strict, it requires two logical volumes that are ready to be used. No special preparation is needed for these volumes other than following the minimum size requirements for data and journal. The API call looks like:: ceph-volume prepare --filestore --data volume_group/lv_name --journal journal The ``--data`` value *must* be a volume group name and a logical volume name separated by a ``/``. Since logical volume names are not enforced for uniqueness, this prevents using the wrong volume. The ``--journal`` can be either a logical volume *or* a partition. When using a partition, it *must* contain a ``PARTUUID`` discoverable by ``blkid``, so that it can later be identified correctly regardless of the device name (or path). When using a partition, this is how it would look for ``/dev/sdc1``:: ceph-volume prepare --filestore --data volume_group/lv_name --journal /dev/sdc1 For a logical volume, just like for ``--data``, a volume group and logical volume name are required:: ceph-volume prepare --filestore --data volume_group/lv_name --journal volume_group/journal_lv A generated uuid is used to ask the cluster for a new OSD. These two pieces are crucial for identifying an OSD and will later be used throughout the :ref:`ceph-volume-lvm-activate` process. The OSD data directory is created using the following convention:: /var/lib/ceph/osd/- At this point the data volume is mounted at this location, and the journal volume is linked:: ln -s /path/to/journal /var/lib/ceph/osd/-/journal The monmap is fetched using the bootstrap key from the OSD:: /usr/bin/ceph --cluster ceph --name client.bootstrap-osd --keyring /var/lib/ceph/bootstrap-osd/ceph.keyring mon getmap -o /var/lib/ceph/osd/-/activate.monmap ``ceph-osd`` will be called to populate the OSD directory, that is already mounted, re-using all the pieces of information from the initial steps:: ceph-osd --cluster ceph --mkfs --mkkey -i \ --monmap /var/lib/ceph/osd/-/activate.monmap --osd-data \ /var/lib/ceph/osd/- --osd-journal /var/lib/ceph/osd/-/journal \ --osd-uuid --keyring /var/lib/ceph/osd/-/keyring \ --setuser ceph --setgroup ceph .. _ceph-volume-lvm-partitions: Partitioning ------------ ``ceph-volume lvm`` does not currently create partitions from a whole device. If using device partitions the only requirement is that they contain the ``PARTUUID`` and that it is discoverable by ``blkid``. Both ``fdisk`` and ``parted`` will create that automatically for a new partition. For example, using a new, unformatted drive (``/dev/sdd`` in this case) we can use ``parted`` to create a new partition. First we list the device information:: $ parted --script /dev/sdd print Model: VBOX HARDDISK (scsi) Disk /dev/sdd: 11.5GB Sector size (logical/physical): 512B/512B Disk Flags: This device is not even labeled yet, so we can use ``parted`` to create a ``gpt`` label before we create a partition, and verify again with ``parted print``:: $ parted --script /dev/sdd mklabel gpt $ parted --script /dev/sdd print Model: VBOX HARDDISK (scsi) Disk /dev/sdd: 11.5GB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: Now lets create a single partition, and verify later if ``blkid`` can find a ``PARTUUID`` that is needed by ``ceph-volume``:: $ parted --script /dev/sdd mkpart primary 1 100% $ blkid /dev/sdd1 /dev/sdd1: PARTLABEL="primary" PARTUUID="16399d72-1e1f-467d-96ee-6fe371a7d0d4" .. _ceph-volume-lvm-existing-osds: Existing OSDs ------------- For existing clusters that want to use this new system and have OSDs that are already running there are a few things to take into account: .. warning:: this process will forcefully format the data device, destroying existing data, if any. * OSD paths should follow this convention:: /var/lib/ceph/osd/- * Preferably, no other mechanisms to mount the volume should exist, and should be removed (like fstab mount points) * There is currently no support for encrypted volumes The one time process for an existing OSD, with an ID of 0 and using a ``"ceph"`` cluster name would look like (the following command will **destroy any data** in the OSD):: ceph-volume lvm prepare --filestore --osd-id 0 --osd-fsid E3D291C1-E7BF-4984-9794-B60D9FA139CB The command line tool will not contact the monitor to generate an OSD ID and will format the LVM device in addition to storing the metadata on it so that it can later be startednot contact the monitor to generate an OSD ID and will format the LVM device in addition to storing the metadata on it so that it can later be started (for detailed metadata description see :ref:`ceph-volume-lvm-tags`). .. _ceph-volume-lvm-prepare_bluestore: ``bluestore`` ------------- This subcommand is planned but not currently implemented. Storing metadata ---------------- The following tags will get applied as part of the prepartion process regardless of the type of volume (journal or data) and also regardless of the OSD backend: * ``cluster_fsid`` * ``data_device`` * ``journal_device`` * ``encrypted`` * ``osd_fsid`` * ``osd_id`` * ``block`` * ``db`` * ``wal`` * ``lockbox_device`` .. note:: For the complete lvm tag conventions see :ref:`ceph-volume-lvm-tag-api` Summary ------- To recap the ``prepare`` process: #. Accept only logical volumes for data and journal (both required) #. Generate a UUID for the OSD #. Ask the monitor get an OSD ID reusing the generated UUID #. OSD data directory is created and data volume mounted #. Journal is symlinked from data volume to journal location #. monmap is fetched for activation #. devices is mounted and data directory is populated by ``ceph-osd`` #. data and journal volumes are assigned all the Ceph metadata using lvm tags