When several VMs had to migrate, but some of them failed, there's no quick way to know from the Migration resource status. 

It will list the succeeded VMs in completedMigrations with 'phase: Completed', but will not mention the failed VMs.

status:
  namespaces:
  - completedMigrations:
    - windows-11-vm-1769098130-0115912
    name: storage-migration-test-storage-class-migration
    phase: Completed

4.21.0

Always, if some VMs can't migrate

1 regular VM + 1 VM from some known bug that prevents migrations 

No way to know if Migration overall succeeded or failed.
Need to check the list of completedMigrations.

Migration resource reports "Succeeded"=False if even one VM failed to migrate, and "Succeeded"=True if all VMs migrated.