Exemplary methods, systems, and computer program product embodiments for migrating existing data from a source storage controller to a target storage controller, each associated with a data processing storage subsystem, using a processor device in communication with a memory device, are provided. The target storage controller is configured with at least one target volume having pass-through support to a source volume of the source storage controller. An input/output (I/O) path to the existing data through the target storage controller is configured. The I/O path is added to an existing I/O path connected to the existing data using an operating system (OS) operational on at least one host in communication between the source and target storage controllers. The OS is adapted for I/O multipath support. Upon completion of data migration, the existing I/O path is removed.