ceph/doc/cephfs/experimental-features.rst

=====================
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.

Inline data has been declared deprecated for the Octopus release, and will
likely be removed altogether in the Q release.

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`.

LazyIO
------
LazyIO relaxes POSIX semantics. Buffered reads/writes are allowed even when a
file is opened by multiple applications on multiple clients. Applications are
responsible for managing cache coherency themselves.