There is one case in which the standby secondary MDS becomes the primary MDS to continue operation. This case occurs if both the primary MDS and secondary MDS are set up as operable and the primary MDS fails by node down. In this case, the following process is performed:
Switching the secondary MDS to the primary MDS
The secondary MDS operates as the primary MDS in place of the primary MDS that has failed.
The new primary MDS replays the update log to ensure consistency of the file system.
Resuming processing after MDS switching
The AC sends a processing request to the new primary MDS. Until that request is accepted, all access to the file system is blocked.
Restarting the failed MDS
Usually, the MDS is restarted as the secondary MDS.
