vCenter Server displays migration recommendations on the Storage DRS Recommendations page for datastore clusters that have manual automation mode.
The system provides as many recommendations as necessary to enforce Storage DRS rules and to balance the space and I/O resources of the datastore cluster. Each recommendation includes the virtual machine name, the virtual disk name, the name of the datastore cluster, the source datastore, the destination datastore, and a reason for the recommendation.
Balance datastore space use
Balance datastore I/O load
Storage DRS makes mandatory recommendations for migration in the following situations:
The datastore is out of space.
Anti-affinity or affinity rules are being violated.
The datastore is entering maintenance mode and must be evacuated.
In addition, optional recommendations are made when a datastore is close to running out of space or when adjustments should be made for space and I/O load balancing.
Storage DRS considers moving virtual machines that are powered off or powered on for space balancing. Storage DRS includes powered-off virtual machines with snapshots in these considerations.