PendingReleaseNotes

>=17.0.0

* `ceph-mgr-modules-core` debian package does not recommend `ceph-mgr-rook`
  anymore. As the latter depends on `python3-numpy` which cannot be imported in
  different Python sub-interpreters multi-times if the version of
  `python3-numpy` is older than 1.19. Since `apt-get` installs the `Recommends`
  packages by default, `ceph-mgr-rook` was always installed along with
  `ceph-mgr` debian package as an indirect dependency. If your workflow depends
  on this behavior, you might want to install `ceph-mgr-rook` separately.

* A new library is available, libcephsqlite. It provides a SQLite Virtual File
  System (VFS) on top of RADOS. The database and journals are striped over
  RADOS across multiple objects for virtually unlimited scaling and throughput
  only limited by the SQLite client. Applications using SQLite may change to
  the Ceph VFS with minimal changes, usually just by specifying the alternate
  VFS. We expect the library to be most impactful and useful for applications
  that were storing state in RADOS omap, especially without striping which
  limits scalability.

* MDS upgrades no longer require stopping all standby MDS daemons before
  upgrading the sole active MDS for a file system.

* CephFS: Failure to replay the journal by a standby-replay daemon will now
  cause the rank to be marked damaged.

* RGW: It is possible to specify ssl options and ciphers for beast frontend now.
  The default ssl options setting is "no_sslv2:no_sslv3:no_tlsv1:no_tlsv1_1".
  If you want to return back the old behavior add 'ssl_options=' (empty) to
  ``rgw frontends`` configuration.

* fs: A file system can be created with a specific ID ("fscid"). This is useful
  in certain recovery scenarios, e.g., monitor database lost and rebuilt, and
  the restored file system is expected to have the same ID as before.

>=16.2.15
----------
* `ceph config dump --format <json|xml>` output will display the localized
  option names instead of its normalized version. For e.g.,
  "mgr/prometheus/x/server_port" will be displayed instead of
  "mgr/prometheus/server_port". This matches the output of the non pretty-print
  formatted version of the command.

* CEPHFS: MDS evicts clients which are not advancing their request tids which causes
  a large buildup of session metadata resulting in the MDS going read-only due to
  the RADOS operation exceeding the size threshold. `mds_session_metadata_threshold`
  config controls the maximum size that a (encoded) session metadata can grow.

* RADOS: `get_pool_is_selfmanaged_snaps_mode` C++ API has been deprecated
  due to being prone to false negative results.  It's safer replacement is
  `pool_is_in_selfmanaged_snaps_mode`.

>= 16.2.14
----------

* CEPHFS: After recovering a Ceph File System post following the disaster recovery
  procedure, the recovered files under `lost+found` directory can now be deleted.

* `ceph mgr dump` command now displays the name of the mgr module that
  registered a RADOS client in the `name` field added to elements of the
  `active_clients` array. Previously, only the address of a module's RADOS
  client was shown in the `active_clients` array.

>=16.2.12
---------

* CEPHFS: Rename the `mds_max_retries_on_remount_failure` option to
  `client_max_retries_on_remount_failure` and move it from mds.yaml.in to
  mds-client.yaml.in because this option was only used by MDS client from its
  birth.

* `ceph mgr dump` command now outputs `last_failure_osd_epoch` and
  `active_clients` fields at the top level.  Previously, these fields were
  output under `always_on_modules` field.

>=16.2.11
--------

* Cephfs: The 'AT_NO_ATTR_SYNC' macro is deprecated, please use the standard
  'AT_STATX_DONT_SYNC' macro. The 'AT_NO_ATTR_SYNC' macro will be removed in
  the future.
* Trimming of PGLog dups is now controlled by the size instead of the version.
  This fixes the PGLog inflation issue that was happening when the on-line
  (in OSD) trimming got jammed after a PG split operation. Also, a new off-line
  mechanism has been added: `ceph-objectstore-tool` got `trim-pg-log-dups` op
  that targets situations where OSD is unable to boot due to those inflated dups.
  If that is the case, in OSD logs the "You can be hit by THE DUPS BUG" warning
  will be visible.
  Relevant tracker: https://tracker.ceph.com/issues/53729
* RBD: `rbd device unmap` command gained `--namespace` option.  Support for
  namespaces was added to RBD in Nautilus 14.2.0 and it has been possible to
  map and unmap images in namespaces using the `image-spec` syntax since then
  but the corresponding option available in most other commands was missing.
* RGW: Compression is now supported for objects uploaded with Server-Side Encryption.
  When both are enabled, compression is applied before encryption.
* RGW: the "pubsub" functionality for storing bucket notifications inside Ceph
  is removed. Together with it, the "pubsub" zone should not be used anymore.
  The REST operations, as well as radosgw-admin commands for manipulating
  subscriptions, as well as fetching and acking the notifications are removed 
  as well.
  In case that the endpoint to which the notifications are sent maybe down or 
  disconnected, it is recommended to use persistent notifications to guarantee 
  the delivery of the notifications. In case the system that consumes the 
  notifications needs to pull them (instead of the notifications be pushed 
  to it), an external message bus (e.g. rabbitmq, Kafka) should be used for 
  that purpose.
* RGW: The serialized format of notification and topics has changed, so that 
  new/updated topics will be unreadable by old RGWs. We recommend completing 
  the RGW upgrades before creating or modifying any notification topics.
* RBD: Trailing newline in passphrase files (`<passphrase-file>` argument in
  `rbd encryption format` command and `--encryption-passphrase-file` option
  in other commands) is no longer stripped.
* RBD: Support for layered client-side encryption is added.  Cloned images
  can now be encrypted each with its own encryption format and passphrase,
  potentially different from that of the parent image.  The efficient
  copy-on-write semantics intrinsic to unformatted (regular) cloned images
  are retained.
* CEPHFS: Rename the `mds_max_retries_on_remount_failure` option to
  `client_max_retries_on_remount_failure` and move it from mds.yaml.in to
  mds-client.yaml.in because this option was only used by MDS client from its
  birth.
* The `perf dump` and `perf schema` commands are deprecated in favor of new
  `counter dump` and `counter schema` commands. These new commands add support
  for labeled perf counters and also emit existing unlabeled perf counters. Some
  unlabeled perf counters became labeled in this release, with more to follow in
  future releases; such converted perf counters are no longer emitted by the
  `perf dump` and `perf schema` commands.
* `ceph mgr dump` command now outputs `last_failure_osd_epoch` and
  `active_clients` fields at the top level.  Previously, these fields were
  output under `always_on_modules` field.
* RBD: All rbd-mirror daemon perf counters became labeled and as such are now
  emitted only by the new `counter dump` and `counter schema` commands.  As part
  of the conversion, many also got renamed to better disambiguate journal-based
  and snapshot-based mirroring.
* RBD: list-watchers C++ API (`Image::list_watchers`) now clears the passed
  `std::list` before potentially appending to it, aligning with the semantics
  of the corresponding C API (`rbd_watchers_list`).
* Telemetry: Users who are opted-in to telemetry can also opt-in to
  participating in a leaderboard in the telemetry public
  dashboards (https://telemetry-public.ceph.com/). Users can now also add a
  description of the cluster to publicly appear in the leaderboard.
  For more details, see:
  https://docs.ceph.com/en/latest/mgr/telemetry/#leaderboard
  See a sample report with `ceph telemetry preview`.
  Opt-in to telemetry with `ceph telemetry on`.
  Opt-in to the leaderboard with
  `ceph config set mgr mgr/telemetry/leaderboard true`.
  Add leaderboard description with:
  `ceph config set mgr mgr/telemetry/leaderboard_description ‘Cluster description’`.
* CEPHFS: After recovering a Ceph File System post following the disaster recovery
  procedure, the recovered files under `lost+found` directory can now be deleted.
* core: cache-tiering is now deprecated.
* mgr/snap_schedule: The snap-schedule mgr module now retains one less snapshot
  than the number mentioned against the config tunable `mds_max_snaps_per_dir`
  so that a new snapshot can be created and retained during the next schedule
  run.

>=16.2.8
--------

* RGW: The behavior for Multipart Upload was modified so that only 
  CompleteMultipartUpload notification is sent at the end of the multipart upload. 
  The POST notification at the beginning of the upload, and PUT notifications that 
  were sent on each part are not sent anymore.

* MON/MGR: Pools can now be created with `--bulk` flag. Any pools created with `bulk`
  will use a profile of the `pg_autoscaler` that provides more performance from the start.
  However, any pools created without the `--bulk` flag will remain using it's old behavior
  by default. For more details, see:

  https://docs.ceph.com/en/latest/rados/operations/placement-groups/

* MGR: The pg_autoscaler can now be turned `on` and `off` globally
  with the `noautoscale` flag. By default this flag is unset and
  the default pg_autoscale mode remains the same.
  For more details, see:

  https://docs.ceph.com/en/latest/rados/operations/placement-groups/

* A health warning will now be reported if the ``require-osd-release`` flag is not
  set to the appropriate release after a cluster upgrade.

>=16.2.7
--------
* Critical bug in OMAP format upgrade is fixed. This could cause data corruption
  (improperly formatted OMAP keys) after pre-Pacific cluster upgrade if
  bluestore-quick-fix-on-mount parameter is set to true or ceph-bluestore-tool's
  quick-fix/repair commands are invoked.
  Relevant tracker: https://tracker.ceph.com/issues/53062

* MGR: The pg_autoscaler will use the 'scale-up' profile as the default profile.
  16.2.6 changed the default profile to 'scale-down' but we ran into issues
  with the device_health_metrics pool consuming too many PGs, which is not ideal
  for performance. So we will continue to use the 'scale-up' profile by default,
  until we implement a limit on the number of PGs default pools should consume,
  in combination with the 'scale-down' profile.

>=16.2.6
--------

* MGR: The pg_autoscaler has a new default 'scale-down' profile which provides more
  performance from the start for new pools (for newly created clusters).
  Existing clusters will retain the old behavior, now called the 'scale-up' profile.
  For more details, see:

  https://docs.ceph.com/en/latest/rados/operations/placement-groups/
* Cephadm: ``osd_memory_target_autotune`` will be enabled by default which will set
  ``mgr/cephadm/autotune_memory_target_ratio`` to ``0.7`` of total RAM. This will be
  unsuitable for hyperconverged infrastructures. For hyperconverged Ceph, please refer
  to the documentation or set ``mgr/cephadm/autotune_memory_target_ratio`` to ``0.2``.

>=16.0.0
--------

* RGW: S3 bucket notification events now contain an `eTag` key instead of `etag`,
  and eventName values no longer carry the `s3:` prefix, fixing deviations from
  the message format observed on AWS.
* `ceph-mgr-modules-core` debian package does not recommend `ceph-mgr-rook`
  anymore. As the latter depends on `python3-numpy` which cannot be imported in
  different Python sub-interpreters multi-times if the version of
  `python3-numpy` is older than 1.19. Since `apt-get` installs the `Recommends`
  packages by default, `ceph-mgr-rook` was always installed along with
  `ceph-mgr` debian package as an indirect dependency. If your workflow depends
  on this behavior, you might want to install `ceph-mgr-rook` separately.

* mgr/nfs: ``nfs`` module is moved out of volumes plugin. Prior using the
  ``ceph nfs`` commands, ``nfs`` mgr module must be enabled.

* volumes/nfs: The ``cephfs`` cluster type has been removed from the
  ``nfs cluster create`` subcommand. Clusters deployed by cephadm can
  support an NFS export of both ``rgw`` and ``cephfs`` from a single
  NFS cluster instance.

* The ``nfs cluster update`` command has been removed.  You can modify
  the placement of an existing NFS service (and/or its associated
  ingress service) using ``orch ls --export`` and ``orch apply -i
  ...``.

* The ``orch apply nfs`` command no longer requires a pool or
  namespace argument. We strongly encourage users to use the defaults
  so that the ``nfs cluster ls`` and related commands will work
  properly.

* The ``nfs cluster delete`` and ``nfs export delete`` commands are
  deprecated and will be removed in a future release.  Please use
  ``nfs cluster rm`` and ``nfs export rm`` instead.

* The ``nfs export create`` CLI arguments have changed, with the
  *fsname* or *bucket-name* argument position moving to the right of
  *the *cluster-id* and *pseudo-path*.  Consider transitioning to
  *using named arguments instead of positional arguments (e.g., ``ceph
  *nfs export create cephfs --cluster-id mycluster --pseudo-path /foo
  *--fsname myfs`` instead of ``ceph nfs export create cephfs
  *mycluster /foo myfs`` to ensure correct behavior with any
  *version.

* mgr-pg_autoscaler: Autoscaler will now start out by scaling each
  pool to have a full complements of pgs from the start and will only
  decrease it when other pools need more pgs due to increased usage.
  This improves out of the box performance of Ceph by allowing more PGs 
  to be created for a given pool.

* CephFS: Disabling allow_standby_replay on a file system will also stop all
  standby-replay daemons for that file system.

* New bluestore_rocksdb_options_annex config parameter. Complements
  bluestore_rocksdb_options and allows setting rocksdb options without repeating
  the existing defaults.
* The cephfs addes two new CDentry tags, 'I' --> 'i' and 'L' --> 'l', and
  on-RADOS metadata is no longer backwards compatible after upgraded to Pacific
  or a later release.

* $pid expansion in config paths like `admin_socket` will now properly expand
  to the daemon pid for commands like `ceph-mds` or `ceph-osd`. Previously only
  `ceph-fuse`/`rbd-nbd` expanded `$pid` with the actual daemon pid.

* The allowable options for some "radosgw-admin" commands have been changed.

  * "mdlog-list", "datalog-list", "sync-error-list" no longer accepts
    start and end dates, but does accept a single optional start marker.
  * "mdlog-trim", "datalog-trim", "sync-error-trim" only accept a
    single marker giving the end of the trimmed range.
  * Similarly the date ranges and marker ranges have been removed on
    the RESTful DATALog and MDLog list and trim operations.

* ceph-volume: The ``lvm batch` subcommand received a major rewrite. This closed
  a number of bugs and improves usability in terms of size specification and
  calculation, as well as idempotency behaviour and disk replacement process.
  Please refer to https://docs.ceph.com/en/latest/ceph-volume/lvm/batch/ for
  more detailed information.

* Configuration variables for permitted scrub times have changed.  The legal
  values for ``osd_scrub_begin_hour`` and ``osd_scrub_end_hour`` are 0 - 23.
  The use of 24 is now illegal.  Specifying ``0`` for both values causes every
  hour to be allowed.  The legal vaues for ``osd_scrub_begin_week_day`` and
  ``osd_scrub_end_week_day`` are 0 - 6.  The use of 7 is now illegal.
  Specifying ``0`` for both values causes every day of the week to be allowed.

* Multiple file systems in a single Ceph cluster is now stable. New Ceph clusters
  enable support for multiple file systems by default. Existing clusters
  must still set the "enable_multiple" flag on the fs. Please see the CephFS
  documentation for more information.

* volume/nfs: Recently "ganesha-" prefix from cluster id and nfs-ganesha common
  config object was removed, to ensure consistent namespace across different
  orchestrator backends. Please delete any existing nfs-ganesha clusters prior
  to upgrading and redeploy new clusters after upgrading to Pacific.

* A new health check, DAEMON_OLD_VERSION, will warn if different versions of Ceph are running
  on daemons. It will generate a health error if multiple versions are detected.
  This condition must exist for over mon_warn_older_version_delay (set to 1 week by default) in order for the
  health condition to be triggered.  This allows most upgrades to proceed
  without falsely seeing the warning.  If upgrade is paused for an extended
  time period, health mute can be used like this
  "ceph health mute DAEMON_OLD_VERSION --sticky".  In this case after
  upgrade has finished use "ceph health unmute DAEMON_OLD_VERSION".

* MGR: progress module can now be turned on/off, using the commands:
  ``ceph progress on`` and ``ceph progress off``.
* An AWS-compliant API: "GetTopicAttributes" was added to replace the existing "GetTopic" API. The new API
  should be used to fetch information about topics used for bucket notifications.

* librbd: The shared, read-only parent cache's config option ``immutable_object_cache_watermark`` now has been updated
  to property reflect the upper cache utilization before space is reclaimed. The default ``immutable_object_cache_watermark``
  now is ``0.9``. If the capacity reaches 90% the daemon will delete cold cache.
* The ceph_volume_client.py library used for manipulating legacy "volumes" in
  CephFS is removed. All remaining users should use the "fs volume" interface
  exposed by the ceph-mgr:
  https://docs.ceph.com/en/latest/cephfs/fs-volumes/

* An AWS-compliant API: "GetTopicAttributes" was added to replace the existing 
  "GetTopic" API. The new API should be used to fetch information about topics 
  used for bucket notifications.

* librbd: The shared, read-only parent cache's config option 
  ``immutable_object_cache_watermark`` has now been updated to properly reflect 
  the upper cache utilization before space is reclaimed. The default 
  ``immutable_object_cache_watermark`` is now ``0.9``. If the capacity reaches 
  90% the daemon will delete cold cache.

* OSD: the option ``osd_fast_shutdown_notify_mon`` has been introduced to allow
  the OSD to notify the monitor it is shutting down even if ``osd_fast_shutdown``
  is enabled. This helps with the monitor logs on larger clusters, that may get
  many 'osd.X reported immediately failed by osd.Y' messages, and confuse tools.
* rgw/kms/vault: the transit logic has been revamped to better use
  the transit engine in vault.  To take advantage of this new
  functionality configuration changes are required.  See the current
  documentation (radosgw/vault) for more details.

* Scubs are more aggressive in trying to find more simultaneous possible PGs within osd_max_scrubs limitation.
  It is possible that increasing osd_scrub_sleep may be necessary to maintain client responsiveness.
* OSD: the option ``osd_fast_shutdown_notify_mon`` has been introduced to allow
  the OSD to notify the monitor it is shutting down even if ``osd_fast_shutdown``
  is enabled. This helps with the monitor logs on larger clusters, that may get
  many 'osd.X reported immediately failed by osd.Y' messages, and confuse tools.

* The mclock scheduler has been refined. A set of built-in profiles are now available that
  provide QoS between the internal and external clients of Ceph. To enable the mclock
  scheduler, set the config option "osd_op_queue" to "mclock_scheduler". The
  "high_client_ops" profile is enabled by default, and allocates more OSD bandwidth to
  external client operations than to internal client operations (such as background recovery
  and scrubs). Other built-in profiles include "high_recovery_ops" and "balanced". These
  built-in profiles optimize the QoS provided to clients of mclock scheduler.

* Version 2 of the cephx authentication protocol (``CEPHX_V2`` feature bit) is
  now required by default.  It was introduced in 2018, adding replay attack
  protection for authorizers and making msgr v1 message signatures stronger
  (CVE-2018-1128 and CVE-2018-1129).  Support is present in Jewel 10.2.11,
  Luminous 12.2.6, Mimic 13.2.1, Nautilus 14.2.0 and later; upstream kernels
  4.9.150, 4.14.86, 4.19 and later; various distribution kernels, in particular
  CentOS 7.6 and later.  To enable older clients, set ``cephx_require_version``
  and ``cephx_service_require_version`` config options to 1.

* rgw: The Civetweb frontend is now deprecated and will be removed in Quincy.

>=15.0.0
--------

* MON: The cluster log now logs health detail every ``mon_health_to_clog_interval``,
  which has been changed from 1hr to 10min. Logging of health detail will be
  skipped if there is no change in health summary since last known.

* The ``ceph df`` command now lists the number of pgs in each pool.

* Monitors now have config option ``mon_allow_pool_size_one``, which is disabled
  by default. However, if enabled, user now have to pass the
  ``--yes-i-really-mean-it`` flag to ``osd pool set size 1``, if they are really
  sure of configuring pool size 1.

* librbd now inherits the stripe unit and count from its parent image upon creation.
  This can be overridden by specifying different stripe settings during clone creation.

* The balancer is now on by default in upmap mode. Since upmap mode requires
  ``require_min_compat_client`` luminous, new clusters will only support luminous
  and newer clients by default. Existing clusters can enable upmap support by running
  ``ceph osd set-require-min-compat-client luminous``. It is still possible to turn
  the balancer off using the ``ceph balancer off`` command. In earlier versions,
  the balancer was included in the ``always_on_modules`` list, but needed to be
  turned on explicitly using the ``ceph balancer on`` command.

* MGR: the "cloud" mode of the diskprediction module is not supported anymore
  and the ``ceph-mgr-diskprediction-cloud`` manager module has been removed. This
  is because the external cloud service run by ProphetStor is no longer accessible
  and there is no immediate replacement for it at this time. The "local" prediction
  mode will continue to be supported.

* Cephadm: There were a lot of small usability improvements and bug fixes:

  * Grafana when deployed by Cephadm now binds to all network interfaces.
  * ``cephadm check-host`` now prints all detected problems at once.
  * Cephadm now calls ``ceph dashboard set-grafana-api-ssl-verify false``
    when generating an SSL certificate for Grafana.
  * The Alertmanager is now correctly pointed to the Ceph Dashboard
  * ``cephadm adopt`` now supports adopting an Alertmanager
  * ``ceph orch ps`` now supports filtering by service name
  * ``ceph orch host ls`` now marks hosts as offline, if they are not
    accessible.

* Cephadm can now deploy NFS Ganesha services. For example, to deploy NFS with
  a service id of mynfs, that will use the RADOS pool nfs-ganesha and namespace
  nfs-ns::

    ceph orch apply nfs mynfs nfs-ganesha nfs-ns

* Cephadm: ``ceph orch ls --export`` now returns all service specifications in
  yaml representation that is consumable by ``ceph orch apply``. In addition,
  the commands ``orch ps`` and ``orch ls`` now support ``--format yaml`` and
  ``--format json-pretty``.

* CephFS: Automatic static subtree partitioning policies may now be configured
  using the new distributed and random ephemeral pinning extended attributes on
  directories. See the documentation for more information:
  https://docs.ceph.com/docs/master/cephfs/multimds/

* Cephadm: ``ceph orch apply osd`` supports a ``--preview`` flag that prints a preview of
  the OSD specification before deploying OSDs. This makes it possible to
  verify that the specification is correct, before applying it.

* RGW: The ``radosgw-admin`` sub-commands dealing with orphans --
  ``radosgw-admin orphans find``, ``radosgw-admin orphans finish``, and
  ``radosgw-admin orphans list-jobs`` -- have been deprecated. They have
  not been actively maintained and they store intermediate results on
  the cluster, which could fill a nearly-full cluster.  They have been
  replaced by a tool, currently considered experimental,
  ``rgw-orphan-list``.

* RBD: The name of the rbd pool object that is used to store
  rbd trash purge schedule is changed from "rbd_trash_trash_purge_schedule"
  to "rbd_trash_purge_schedule". Users that have already started using
  ``rbd trash purge schedule`` functionality and have per pool or namespace
  schedules configured should copy "rbd_trash_trash_purge_schedule"
  object to "rbd_trash_purge_schedule" before the upgrade and remove
  "rbd_trash_purge_schedule" using the following commands in every RBD
  pool and namespace where a trash purge schedule was previously
  configured::

    rados -p <pool-name> [-N namespace] cp rbd_trash_trash_purge_schedule rbd_trash_purge_schedule
    rados -p <pool-name> [-N namespace] rm rbd_trash_trash_purge_schedule

  or use any other convenient way to restore the schedule after the
  upgrade.

* librbd: The shared, read-only parent cache has been moved to a separate librbd
  plugin. If the parent cache was previously in-use, you must also instruct
  librbd to load the plugin by adding the following to your configuration::

    rbd_plugins = parent_cache

* Monitors now have a config option ``mon_osd_warn_num_repaired``, 10 by default.
  If any OSD has repaired more than this many I/O errors in stored data a
 ``OSD_TOO_MANY_REPAIRS`` health warning is generated.

* Introduce commands that manipulate required client features of a file system::

    ceph fs required_client_features <fs name> add <feature>
    ceph fs required_client_features <fs name> rm <feature>
    ceph fs feature ls

* OSD: A new configuration option ``osd_compact_on_start`` has been added which triggers
  an OSD compaction on start. Setting this option to ``true`` and restarting an OSD
  will result in an offline compaction of the OSD prior to booting.

* OSD: the option named ``bdev_nvme_retry_count`` has been removed. Because
  in SPDK v20.07, there is no easy access to bdev_nvme options, and this
  option is hardly used, so it was removed.

* Now when noscrub and/or nodeep-scrub flags are set globally or per pool,
  scheduled scrubs of the type disabled will be aborted. All user initiated
  scrubs are NOT interrupted.

* Alpine build related script, documentation and test have been removed since
  the most updated APKBUILD script of Ceph is already included by Alpine Linux's
  aports repository.

* fs: Names of new FSs, volumes, subvolumes and subvolume groups can only
  contain alphanumeric and ``-``, ``_`` and ``.`` characters. Some commands
  or CephX credentials may not work with old FSs with non-conformant names.

* It is now possible to specify the initial monitor to contact for Ceph tools
  and daemons using the ``mon_host_override`` config option or
  ``--mon-host-override <ip>`` command-line switch. This generally should only
  be used for debugging and only affects initial communication with Ceph's
  monitor cluster.

* `blacklist` has been replaced with `blocklist` throughout.  The following commands have changed:

  - ``ceph osd blacklist ...`` are now ``ceph osd blocklist ...``
  - ``ceph <tell|daemon> osd.<NNN> dump_blacklist`` is now ``ceph <tell|daemon> osd.<NNN> dump_blocklist``

* The following config options have changed:

  - ``mon osd blacklist default expire`` is now ``mon osd blocklist default expire``
  - ``mon mds blacklist interval`` is now ``mon mds blocklist interval``
  - ``mon mgr blacklist interval`` is now ''mon mgr blocklist interval``
  - ``rbd blacklist on break lock`` is now ``rbd blocklist on break lock``
  - ``rbd blacklist expire seconds`` is now ``rbd blocklist expire seconds``
  - ``mds session blacklist on timeout`` is now ``mds session blocklist on timeout``
  - ``mds session blacklist on evict`` is now ``mds session blocklist on evict``

* CephFS: Compatibility code for old on-disk format of snapshot has been removed.
  Current on-disk format of snapshot was introduced by Mimic release. If there
  are any snapshots created by Ceph release older than Mimic. Before upgrading,
  either delete them all or scrub the whole filesystem:

    ceph daemon <mds of rank 0> scrub_path / force recursive repair
    ceph daemon <mds of rank 0> scrub_path '~mdsdir' force recursive repair

* CephFS: Scrub is supported in multiple active mds setup. MDS rank 0 handles
  scrub commands, and forward scrub to other mds if necessary.

* The following librados API calls have changed:

  - ``rados_blacklist_add`` is now ``rados_blocklist_add``; the former will issue a deprecation warning and be removed in a future release.
  - ``rados.blacklist_add`` is now ``rados.blocklist_add`` in the C++ API.

* The JSON output for the following commands now shows ``blocklist`` instead of ``blacklist``:

  - ``ceph osd dump``
  - ``ceph <tell|daemon> osd.<N> dump_blocklist``

* caps: MON and MDS caps can now be used to restrict client's ability to view
  and operate on specific Ceph file systems. The FS can be specificed using
  ``fsname`` in caps. This also affects subcommand ``fs authorize``, the caps
  produce by it will be specific to the FS name passed in its arguments.

* fs: root_squash flag can be set in MDS caps. It disallows file system
  operations that need write access for clients with uid=0 or gid=0. This
  feature should prevent accidents such as an inadvertent `sudo rm -rf /<path>`.

* fs: "fs authorize" now sets MON cap to "allow <perm> fsname=<fsname>"
      instead of setting it to "allow r" all the time.

* ``ceph pg #.# list_unfound`` output has been enhanced to provide
  might_have_unfound information which indicates which OSDs may
  contain the unfound objects.

* The ``ceph orch apply rgw`` syntax and behavior have changed.  RGW
  services can now be arbitrarily named (it is no longer forced to be
  `realm.zone`).  The ``--rgw-realm=...`` and ``--rgw-zone=...``
  arguments are now optional, which means that if they are omitted, a
  vanilla single-cluster RGW will be deployed.  When the realm and
  zone are provided, the user is now responsible for setting up the
  multisite configuration beforehand--cephadm no longer attempts to
  create missing realms or zones.

* The cephadm NFS support has been simplified to no longer allow the
  pool and namespace where configuration is stored to be customized.
  As a result, the ``ceph orch apply nfs`` command no longer has
  ``--pool`` or ``--namespace`` arguments.

  Existing cephadm NFS deployments (from earlier version of Pacific or
  from Octopus) will be automatically migrated when the cluster is
  upgraded.  Note that the NFS ganesha daemons will be redeployed and
  it is possible that their IPs will change.

* RGW now requires a secure connection to the monitor by default
  (``auth_client_required=cephx`` and ``ms_mon_client_mode=secure``).
  If you have cephx authentication disabled on your cluster, you may
  need to adjust these settings for RGW.