and the scrubbing process is delayed between each read in order to avoid monopolizing
the I/O capacity of the OSD.
The default stride size (``osd_deep_scrub_stride``) was 512 KBytes, and is now 4 MBytes.
+ * RADOS: When an OSD is overloaded with queued snap-trim operations, no
+ regular (non-urgent) scrubs will be scheduled on that OSD. This is
+ determined by comparing the total snap-trim queue lengths for all PGs
+ for which the OSD is a primary against ``osd_scrub_queued_snaptrims_limit``,
+ which defaults to 500.
+ This restriction does not apply to operator-initiated scrubs, nor to repair scrubs.
+ It can be disabled by setting ``osd_scrub_queued_snaptrims_limit`` to 0.
+>=21.0.0
+
+* CephX: a new key type ``aes256k`` has been introduced to address
+ vulnerabilities in the existing encryption schemes. It is necessary to
+ perform an upgrade of all CephX keys used by daemons or clients. Please see
+ :ref:`cephx-upgrade` for more information.
+* The ``auth_supported`` config has been removed.
+* The monitor map includes new settings relating to CephX: auth_service_cipher,
+ auth_allowed_ciphers, and auth_preferred_cipher. These are used to control
+ which CephX key types may be used in the cluster.
+* A new --key-type argument has been introduced for all commands which produce CephX keys. This includes monitor commands as well as Ceph cluster bootstrap commands like ceph-authtool and monmaptool.
+* The ``mon.`` credential is now authoritatively stored in the Monitor "auth" database. The monitor keyring file is only used as a fallback. The ``ceph-mon`` command now includes a --use-mon-keyring switch for recovery if the ``mon.`` key in the auth database is lost.
+
* RADOS: Stretch mode can now be entered even if the two dividing buckets differ
in weight by a small fraction (default 0.1). This is tunable via
`mon_stretch_max_bucket_weight_delta`.