What is necessary for a successful virtual machine migration in cloud computing?

For a successful virtual machine migration in cloud computing, shared storage between servers is a critical requirement. When a virtual machine (VM) is migrated from one physical host to another, the VM's data—essentially the disk files—need to be accessible during the migration process. If both the source and destination servers can access the same storage, it allows for a seamless transfer of the VM's state without significant downtime.

During migration, the VM can be either moved live (without downtime) or offline (with downtime), but having shared storage simplifies the process. It enables the VM to maintain its state and connections, reducing risks associated with data loss or service interruptions.

The other choices, while relevant to specific types of migrations or scenarios, do not universally apply to all successful migrations. Compatibility with physical servers may be important in a traditional setting or when expanding hybrid architectures, but virtualized environments often abstract away specific hardware dependencies. Similarly, having the same hardware configuration can enhance performance or compatibility, but it's typically not a strict requirement in cloud environments where resources are virtualized and managed differently. Thus, shared storage is a foundational necessity for effective VM migration across disparate environments.