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-
-Experimental Features
-=====================
-
-CephFS includes a number of experimental features which are not fully stabilized
-or qualified for users to turn on in real deployments. We generally do our best
-to clearly demarcate these and fence them off so they cannot be used by mistake.
-
-Some of these features are closer to being done than others, though. We describe
-each of them with an approximation of how risky they are and briefly describe
-what is required to enable them. Note that doing so will *irrevocably* flag maps
-in the monitor as having once enabled this flag to improve debugging and
-support processes.
-
-Inline data
------------
-By default, all CephFS file data is stored in RADOS objects. The inline data
-feature enables small files (generally <2KB) to be stored in the inode
-and served out of the MDS. This may improve small-file performance but increases
-load on the MDS. It is not sufficiently tested to support at this time, although
-failures within it are unlikely to make non-inlined data inaccessible
-
-Inline data has always been off by default and requires setting
-the "inline_data" flag.
-
-
-
-Mantle: Programmable Metadata Load Balancer
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Mantle is a programmable metadata balancer built into the MDS. The idea is to
-protect the mechanisms for balancing load (migration, replication,
-fragmentation) but stub out the balancing policies using Lua. For details, see
-:doc:`/cephfs/mantle`.
-
-Snapshots
----------
-Like multiple active MDSes, CephFS is designed from the ground up to support
-snapshotting of arbitrary directories. There are no known bugs at the time of
-writing, but there is insufficient testing to provide stability guarantees and
-every expansion of testing has generally revealed new issues. If you do enable
-snapshots and experience failure, manual intervention will be needed.
-
-Snapshots are known not to work properly with multiple filesystems (below) in
-some cases. Specifically, if you share a pool for multiple FSes and delete
-a snapshot in one FS, expect to lose snapshotted file data in any other FS using
-snapshots. See the :doc:`/dev/cephfs-snapshots` page for more information.
-
-Snapshots are known not to work with multi-MDS filesystems.
-
-Snapshotting was blocked off with the "allow_new_snaps" flag prior to Firefly.
-
-Multiple filesystems within a Ceph cluster
-------------------------------------------
-Code was merged prior to the Jewel release which enables administrators
-to create multiple independent CephFS filesystems within a single Ceph cluster.
-These independent filesystems have their own set of active MDSes, cluster maps,
-and data. But the feature required extensive changes to data structures which
-are not yet fully qualified, and has security implications which are not all
-apparent nor resolved.
-
-There are no known bugs, but any failures which do result from having multiple
-active filesystems in your cluster will require manual intervention and, so far,
-will not have been experienced by anybody else -- knowledgeable help will be
-extremely limited. You also probably do not have the security or isolation
-guarantees you want or think you have upon doing so.
-
-Note that snapshots and multiple filesystems are *not* tested in combination
-and may not work together; see above.
-
-Multiple filesystems were available starting in the Jewel release candidates
-but were protected behind the "enable_multiple" flag before the final release.
-
-
-Previously experimental features
-================================
-
-Directory Fragmentation
------------------------
-
-Directory fragmentation was considered experimental prior to the *Luminous*
-(12.2.x). It is now enabled by default on new filesystems. To enable directory
-fragmentation on filesystems created with older versions of Ceph, set
-the ``allow_dirfrags`` flag on the filesystem:
-
-::
-
- ceph fs set <filesystem name> allow_dirfrags
-
-Multiple active metadata servers
---------------------------------
-
-Prior to the *Luminous* (12.2.x) release, running multiple active metadata
-servers within a single filesystem was considered experimental. Creating
-multiple active metadata servers is now permitted by default on new
-filesystems.
-
-Filesystems created with older versions of Ceph still require explicitly
-enabling multiple active metadata servers as follows:
-
-::
-
- ceph fs set <filesystem name> allow_multimds
-
-Note that the default size of the active mds cluster (``max_mds``) is
-still set to 1 initially.
-