Migrating more than one datastore into a datastore cluster fails with an error message after the first virtual machine has successfully moved into the datastore cluster.
When you attempt to migrate multiple virtual machines into a datastore cluster, some virtual machines migrate successfully, but migration of subsequent virtual machines fails. vCenter Server displays the error message, Insufficient Disk Space on Datastore.
Until each placement recommendation is applied, the space resources appear to be available to Storage DRS. Therefore, Storage DRS might reallocate space resources to subsequent requests for space.
Retry the failed migration operations one at a time and ensure that each recommendation is applied before requesting the next migration