ceph/doc/mgr/mds_autoscaler.rst

   1 MDS Autoscaler Module
   2 =====================
   3
   4 The MDS Autoscaler Module monitors ``fsmap`` update notifications from the mgr
   5 daemon and takes action to spawn or kill MDS daemons for a file-system as per
   6 changes to the:
   7
   8 - ``max_mds`` config value
   9 - ``standby_count_wanted`` config value
  10 - standby promotions to active MDS state in case of active MDS rank death
  11
  12 Bumping up the ``max_mds`` config option value causes a standby mds to be promoted
  13 to hold an active rank. This leads to a drop in standby mds count. The MDS
  14 Autoscaler module detects this deficit and the orchestrator module is notified
  15 about the required MDS count. The orchestrator back-end then takes necessary
  16 measures to spawn standby MDSs.
  17
  18 Dropping the ``max_mds`` config option causes the orchestrator back-end to kill
  19 standby mds to achieve the new reduced count. Preferably standby mds are chosen
  20 to be killed when the ``max_mds`` count is dropped.
  21
  22 An increment and decrement of the ``standby_count_wanted`` config option value
  23 has a similar effect on the total MDS count. The orchestrator is notified about
  24 the change and necessary action to spawn or kill standby MDSs is taken.
  25
  26 A death of an active MDS rank also causes promotion of a standby mds to occupy
  27 the required active rank. The MDS Autoscaler notices the change in the standby
  28 mds count and a message is passed to the orchestrator to maintain the necessary
  29 MDS count.
  30
  31 NOTE: There is no CLI associated with the MDS Autoscaler Module.