ceph/doc/cephfs/experimental-features.rst

   1 =====================
   2 Experimental Features
   3 =====================
   4
   5 CephFS includes a number of experimental features which are not fully
   6 stabilized or qualified for users to turn on in real deployments. We generally
   7 do our best to clearly demarcate these and fence them off so they cannot be
   8 used by mistake.
   9
  10 Some of these features are closer to being done than others, though. We
  11 describe each of them with an approximation of how risky they are and briefly
  12 describe what is required to enable them. Note that doing so will
  13 *irrevocably* flag maps in the monitor as having once enabled this flag to
  14 improve debugging and support processes.
  15
  16 Inline data
  17 -----------
  18 By default, all CephFS file data is stored in RADOS objects. The inline data
  19 feature enables small files (generally <2KB) to be stored in the inode
  20 and served out of the MDS. This may improve small-file performance but increases
  21 load on the MDS. It is not sufficiently tested to support at this time, although
  22 failures within it are unlikely to make non-inlined data inaccessible
  23
  24 Inline data has always been off by default and requires setting
  25 the ``inline_data`` flag.
  26
  27 Inline data has been declared deprecated for the Octopus release, and will
  28 likely be removed altogether in the Q release.
  29
  30 Mantle: Programmable Metadata Load Balancer
  31 -------------------------------------------
  32
  33 Mantle is a programmable metadata balancer built into the MDS. The idea is to
  34 protect the mechanisms for balancing load (migration, replication,
  35 fragmentation) but stub out the balancing policies using Lua. For details, see
  36 :doc:`/cephfs/mantle`.
  37
  38 LazyIO
  39 ------
  40 LazyIO relaxes POSIX semantics. Buffered reads/writes are allowed even when a
  41 file is opened by multiple applications on multiple clients. Applications are
  42 responsible for managing cache coherency themselves.