How to enable Ignore Storage DRS Affinity Rules for Maintenance Mode
Storage DRS affinity or anti-affinity rules might prevent a datastore from entering maintenance mode. You can ignore these rules when you put a datastore in maintenance mode.
1. In the vSphere Client inventory, right-click a datastore cluster and select Edit Settings. 2. In the right pane of the Edit Datastore Cluster dialog box, select SDRS Automation.