MDS Autoscaler Module¶

The MDS Autoscaler Module monitors fsmap update notifications from the mgr daemon and takes action to spawn or kill MDS daemons for a file-system as per changes to the:

max_mds config value
standby_count_wanted config value
standby promotions to active MDS state in case of active MDS rank death

Bumping up the max_mds config option value causes a standby mds to be promoted to hold an active rank. This leads to a drop in standby mds count. The MDS Autoscaler module detects this deficit and the orchestrator module is notified about the required MDS count. The orchestrator back-end then takes necessary measures to spawn standby MDSs.

Dropping the max_mds config option causes the orchestrator back-end to kill standby mds to achieve the new reduced count. Preferably standby mds are chosen to be killed when the max_mds count is dropped.

An increment and decrement of the standby_count_wanted config option value has a similar effect on the total MDS count. The orchestrator is notified about the change and necessary action to spawn or kill standby MDSs is taken.

A death of an active MDS rank also causes promotion of a standby mds to occupy the required active rank. The MDS Autoscaler notices the change in the standby mds count and a message is passed to the orchestrator to maintain the necessary MDS count.

NOTE: There is no CLI associated with the MDS Autoscaler Module.