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diff --git a/doc/rados/operations/bluestore-migration.rst b/doc/rados/operations/bluestore-migration.rst new file mode 100644 index 000000000..d24782c46 --- /dev/null +++ b/doc/rados/operations/bluestore-migration.rst @@ -0,0 +1,357 @@ +.. _rados_operations_bluestore_migration: + +===================== + BlueStore Migration +===================== +.. warning:: Filestore has been deprecated in the Reef release and is no longer supported. + Please migrate to BlueStore. + +Each OSD must be formatted as either Filestore or BlueStore. However, a Ceph +cluster can operate with a mixture of both Filestore OSDs and BlueStore OSDs. +Because BlueStore is superior to Filestore in performance and robustness, and +because Filestore is not supported by Ceph releases beginning with Reef, users +deploying Filestore OSDs should transition to BlueStore. There are several +strategies for making the transition to BlueStore. + +BlueStore is so different from Filestore that an individual OSD cannot be +converted in place. Instead, the conversion process must use either (1) the +cluster's normal replication and healing support, or (2) tools and strategies +that copy OSD content from an old (Filestore) device to a new (BlueStore) one. + +Deploying new OSDs with BlueStore +================================= + +Use BlueStore when deploying new OSDs (for example, when the cluster is +expanded). Because this is the default behavior, no specific change is +needed. + +Similarly, use BlueStore for any OSDs that have been reprovisioned after +a failed drive was replaced. + +Converting existing OSDs +======================== + +"Mark-``out``" replacement +-------------------------- + +The simplest approach is to verify that the cluster is healthy and +then follow these steps for each Filestore OSD in succession: mark the OSD +``out``, wait for the data to replicate across the cluster, reprovision the OSD, +mark the OSD back ``in``, and wait for recovery to complete before proceeding +to the next OSD. This approach is easy to automate, but it entails unnecessary +data migration that carries costs in time and SSD wear. + +#. Identify a Filestore OSD to replace:: + + ID=<osd-id-number> + DEVICE=<disk-device> + + #. Determine whether a given OSD is Filestore or BlueStore: + + .. prompt:: bash $ + + ceph osd metadata $ID | grep osd_objectstore + + #. Get a current count of Filestore and BlueStore OSDs: + + .. prompt:: bash $ + + ceph osd count-metadata osd_objectstore + +#. Mark a Filestore OSD ``out``: + + .. prompt:: bash $ + + ceph osd out $ID + +#. Wait for the data to migrate off this OSD: + + .. prompt:: bash $ + + while ! ceph osd safe-to-destroy $ID ; do sleep 60 ; done + +#. Stop the OSD: + + .. prompt:: bash $ + + systemctl kill ceph-osd@$ID + + .. _osd_id_retrieval: + +#. Note which device the OSD is using: + + .. prompt:: bash $ + + mount | grep /var/lib/ceph/osd/ceph-$ID + +#. Unmount the OSD: + + .. prompt:: bash $ + + umount /var/lib/ceph/osd/ceph-$ID + +#. Destroy the OSD's data. Be *EXTREMELY CAREFUL*! These commands will destroy + the contents of the device; you must be certain that the data on the device is + not needed (in other words, that the cluster is healthy) before proceeding: + + .. prompt:: bash $ + + ceph-volume lvm zap $DEVICE + +#. Tell the cluster that the OSD has been destroyed (and that a new OSD can be + reprovisioned with the same OSD ID): + + .. prompt:: bash $ + + ceph osd destroy $ID --yes-i-really-mean-it + +#. Provision a BlueStore OSD in place by using the same OSD ID. This requires + you to identify which device to wipe, and to make certain that you target + the correct and intended device, using the information that was retrieved in + the :ref:`"Note which device the OSD is using" <osd_id_retrieval>` step. BE + CAREFUL! Note that you may need to modify these commands when dealing with + hybrid OSDs: + + .. prompt:: bash $ + + ceph-volume lvm create --bluestore --data $DEVICE --osd-id $ID + +#. Repeat. + +You may opt to (1) have the balancing of the replacement BlueStore OSD take +place concurrently with the draining of the next Filestore OSD, or instead +(2) follow the same procedure for multiple OSDs in parallel. In either case, +however, you must ensure that the cluster is fully clean (in other words, that +all data has all replicas) before destroying any OSDs. If you opt to reprovision +multiple OSDs in parallel, be **very** careful to destroy OSDs only within a +single CRUSH failure domain (for example, ``host`` or ``rack``). Failure to +satisfy this requirement will reduce the redundancy and availability of your +data and increase the risk of data loss (or even guarantee data loss). + +Advantages: + +* Simple. +* Can be done on a device-by-device basis. +* No spare devices or hosts are required. + +Disadvantages: + +* Data is copied over the network twice: once to another OSD in the cluster (to + maintain the specified number of replicas), and again back to the + reprovisioned BlueStore OSD. + +"Whole host" replacement +------------------------ + +If you have a spare host in the cluster, or sufficient free space to evacuate +an entire host for use as a spare, then the conversion can be done on a +host-by-host basis so that each stored copy of the data is migrated only once. + +To use this approach, you need an empty host that has no OSDs provisioned. +There are two ways to do this: either by using a new, empty host that is not +yet part of the cluster, or by offloading data from an existing host that is +already part of the cluster. + +Using a new, empty host +^^^^^^^^^^^^^^^^^^^^^^^ + +Ideally the host will have roughly the same capacity as each of the other hosts +you will be converting. Add the host to the CRUSH hierarchy, but do not attach +it to the root: + + +.. prompt:: bash $ + + NEWHOST=<empty-host-name> + ceph osd crush add-bucket $NEWHOST host + +Make sure that Ceph packages are installed on the new host. + +Using an existing host +^^^^^^^^^^^^^^^^^^^^^^ + +If you would like to use an existing host that is already part of the cluster, +and if there is sufficient free space on that host so that all of its data can +be migrated off to other cluster hosts, you can do the following (instead of +using a new, empty host): + +.. prompt:: bash $ + + OLDHOST=<existing-cluster-host-to-offload> + ceph osd crush unlink $OLDHOST default + +where "default" is the immediate ancestor in the CRUSH map. (For +smaller clusters with unmodified configurations this will normally +be "default", but it might instead be a rack name.) You should now +see the host at the top of the OSD tree output with no parent: + +.. prompt:: bash $ + + bin/ceph osd tree + +:: + + ID CLASS WEIGHT TYPE NAME STATUS REWEIGHT PRI-AFF + -5 0 host oldhost + 10 ssd 1.00000 osd.10 up 1.00000 1.00000 + 11 ssd 1.00000 osd.11 up 1.00000 1.00000 + 12 ssd 1.00000 osd.12 up 1.00000 1.00000 + -1 3.00000 root default + -2 3.00000 host foo + 0 ssd 1.00000 osd.0 up 1.00000 1.00000 + 1 ssd 1.00000 osd.1 up 1.00000 1.00000 + 2 ssd 1.00000 osd.2 up 1.00000 1.00000 + ... + +If everything looks good, jump directly to the :ref:`"Wait for the data +migration to complete" <bluestore_data_migration_step>` step below and proceed +from there to clean up the old OSDs. + +Migration process +^^^^^^^^^^^^^^^^^ + +If you're using a new host, start at :ref:`the first step +<bluestore_migration_process_first_step>`. If you're using an existing host, +jump to :ref:`this step <bluestore_data_migration_step>`. + +.. _bluestore_migration_process_first_step: + +#. Provision new BlueStore OSDs for all devices: + + .. prompt:: bash $ + + ceph-volume lvm create --bluestore --data /dev/$DEVICE + +#. Verify that the new OSDs have joined the cluster: + + .. prompt:: bash $ + + ceph osd tree + + You should see the new host ``$NEWHOST`` with all of the OSDs beneath + it, but the host should *not* be nested beneath any other node in the + hierarchy (like ``root default``). For example, if ``newhost`` is + the empty host, you might see something like:: + + $ bin/ceph osd tree + ID CLASS WEIGHT TYPE NAME STATUS REWEIGHT PRI-AFF + -5 0 host newhost + 10 ssd 1.00000 osd.10 up 1.00000 1.00000 + 11 ssd 1.00000 osd.11 up 1.00000 1.00000 + 12 ssd 1.00000 osd.12 up 1.00000 1.00000 + -1 3.00000 root default + -2 3.00000 host oldhost1 + 0 ssd 1.00000 osd.0 up 1.00000 1.00000 + 1 ssd 1.00000 osd.1 up 1.00000 1.00000 + 2 ssd 1.00000 osd.2 up 1.00000 1.00000 + ... + +#. Identify the first target host to convert : + + .. prompt:: bash $ + + OLDHOST=<existing-cluster-host-to-convert> + +#. Swap the new host into the old host's position in the cluster: + + .. prompt:: bash $ + + ceph osd crush swap-bucket $NEWHOST $OLDHOST + + At this point all data on ``$OLDHOST`` will begin migrating to the OSDs on + ``$NEWHOST``. If there is a difference between the total capacity of the + old hosts and the total capacity of the new hosts, you may also see some + data migrate to or from other nodes in the cluster. Provided that the hosts + are similarly sized, however, this will be a relatively small amount of + data. + + .. _bluestore_data_migration_step: + +#. Wait for the data migration to complete: + + .. prompt:: bash $ + + while ! ceph osd safe-to-destroy $(ceph osd ls-tree $OLDHOST); do sleep 60 ; done + +#. Stop all old OSDs on the now-empty ``$OLDHOST``: + + .. prompt:: bash $ + + ssh $OLDHOST + systemctl kill ceph-osd.target + umount /var/lib/ceph/osd/ceph-* + +#. Destroy and purge the old OSDs: + + .. prompt:: bash $ + + for osd in `ceph osd ls-tree $OLDHOST`; do + ceph osd purge $osd --yes-i-really-mean-it + done + +#. Wipe the old OSDs. This requires you to identify which devices are to be + wiped manually. BE CAREFUL! For each device: + + .. prompt:: bash $ + + ceph-volume lvm zap $DEVICE + +#. Use the now-empty host as the new host, and repeat: + + .. prompt:: bash $ + + NEWHOST=$OLDHOST + +Advantages: + +* Data is copied over the network only once. +* An entire host's OSDs are converted at once. +* Can be parallelized, to make possible the conversion of multiple hosts at the same time. +* No host involved in this process needs to have a spare device. + +Disadvantages: + +* A spare host is required. +* An entire host's worth of OSDs will be migrating data at a time. This + is likely to impact overall cluster performance. +* All migrated data still makes one full hop over the network. + +Per-OSD device copy +------------------- +A single logical OSD can be converted by using the ``copy`` function +included in ``ceph-objectstore-tool``. This requires that the host have one or more free +devices to provision a new, empty BlueStore OSD. For +example, if each host in your cluster has twelve OSDs, then you need a +thirteenth unused OSD so that each OSD can be converted before the +previous OSD is reclaimed to convert the next OSD. + +Caveats: + +* This approach requires that we prepare an empty BlueStore OSD but that we do not allocate + a new OSD ID to it. The ``ceph-volume`` tool does not support such an operation. **IMPORTANT:** + because the setup of *dmcrypt* is closely tied to the identity of the OSD, this approach does not + work with encrypted OSDs. + +* The device must be manually partitioned. + +* An unsupported user-contributed script that demonstrates this process may be found here: + https://github.com/ceph/ceph/blob/master/src/script/contrib/ceph-migrate-bluestore.bash + +Advantages: + +* Provided that the 'noout' or the 'norecover'/'norebalance' flags are set on the OSD or the + cluster while the conversion process is underway, little or no data migrates over the + network during the conversion. + +Disadvantages: + +* Tooling is not fully implemented, supported, or documented. + +* Each host must have an appropriate spare or empty device for staging. + +* The OSD is offline during the conversion, which means new writes to PGs + with the OSD in their acting set may not be ideally redundant until the + subject OSD comes up and recovers. This increases the risk of data + loss due to an overlapping failure. However, if another OSD fails before + conversion and startup have completed, the original Filestore OSD can be + started to provide access to its original data. |