>=18.0.0

* RGW's default backend for `rgw_enable_ops_log` changed from RADOS to file.
  The default value of `rgw_ops_log_rados` is now false, and `rgw_ops_log_file_path`
  defaults to "/var/log/ceph/ops-log-$cluster-$name.log".
* The SPDK backend for BlueStore is now able to connect to an NVMeoF target.
  Please note that this is not an officially supported feature.
* RGW's pubsub interface now returns boolean fields using bool. Before this change,
  `/topics/<topic-name>` returns "stored_secret" and "persistent" using a string
  of "true" or "false" with quotes around them. After this change, these fields
  are returned without quotes so they can be decoded as boolean values in JSON.
  The same applies to the `is_truncated` field returned by `/subscriptions/<sub-name>`.
* RGW's response of `Action=GetTopicAttributes&TopicArn=<topic-arn>` REST API now
  returns `HasStoredSecret` and `Persistent` as boolean in the JSON string
  encoded in `Attributes/EndPoint`.
* All boolean fields previously rendered as string by `rgw-admin` command when
  the JSON format is used are now rendered as boolean. If your scripts/tools
  relies on this behavior, please update them accordingly. The impacted field names
  are:
  * absolute
  * add
  * admin
  * appendable
  * bucket_key_enabled
  * delete_marker
  * exists
  * has_bucket_info
  * high_precision_time
  * index
  * is_master
  * is_prefix
  * is_truncated
  * linked
  * log_meta
  * log_op
  * pending_removal
  * read_only
  * retain_head_object
  * rule_exist
  * start_with_full_sync
  * sync_from_all
  * syncstopped
  * system
  * truncated
  * user_stats_sync
* RGW: The beast frontend's HTTP access log line uses a new debug_rgw_access
  configurable. This has the same defaults as debug_rgw, but can now be controlled
  independently.
* RBD: The semantics of compare-and-write C++ API (`Image::compare_and_write`
  and `Image::aio_compare_and_write` methods) now match those of C API.  Both
  compare and write steps operate only on `len` bytes even if the respective
  buffers are larger. The previous behavior of comparing up to the size of
  the compare buffer was prone to subtle breakage upon straddling a stripe
  unit boundary.
* RBD: compare-and-write operation is no longer limited to 512-byte sectors.
  Assuming proper alignment, it now allows operating on stripe units (4M by
  default).

>=17.2.1

* The "BlueStore zero block detection" feature (first introduced to Quincy in
https://github.com/ceph/ceph/pull/43337) has been turned off by default with a
new global configuration called `bluestore_zero_block_detection`. This feature,
intended for large-scale synthetic testing, does not interact well with some RBD
and CephFS features. Any side effects experienced in previous Quincy versions
would no longer occur, provided that the configuration remains set to false.
Relevant tracker: https://tracker.ceph.com/issues/55521

* telemetry: Added new Rook metrics to the 'basic' channel to report Rook's
  version, Kubernetes version, node metrics, etc.
  See a sample report with `ceph telemetry preview`.
  Opt-in with `ceph telemetry on`.

  For more details, see:

  https://docs.ceph.com/en/latest/mgr/telemetry/

>=15.2.17

* OSD: Octopus modified the SnapMapper key format from
  <LEGACY_MAPPING_PREFIX><snapid>_<shardid>_<hobject_t::to_str()>
  to
  <MAPPING_PREFIX><pool>_<snapid>_<shardid>_<hobject_t::to_str()>
  When this change was introduced, 94ebe0e also introduced a conversion
  with a crucial bug which essentially destroyed legacy keys by mapping them
  to
  <MAPPING_PREFIX><poolid>_<snapid>_
  without the object-unique suffix. The conversion is fixed in this release.
  Relevant tracker: https://tracker.ceph.com/issues/5614
  
* Cephadm may now be configured to carry out CephFS MDS upgrades without
reducing ``max_mds`` to 1. Previously, Cephadm would reduce ``max_mds`` to 1 to
avoid having two active MDS modifying on-disk structures with new versions,
communicating cross-version-incompatible messages, or other potential
incompatibilities. This could be disruptive for large-scale CephFS deployments
because the cluster cannot easily reduce active MDS daemons to 1.
NOTE: Staggered upgrade of the mons/mgrs may be necessary to take advantage
of the feature, refer this link on how to perform it:
https://docs.ceph.com/en/quincy/cephadm/upgrade/#staggered-upgrade
Relevant tracker: https://tracker.ceph.com/issues/55715