Concurrent upgrade of all components in storage subsystems

A plurality of upgraded components associated with an upgraded storage subsystem replaces a plurality of existing components associated with an existing storage subsystem. Support for a verify I/O command is created. A target volume is created in the upgraded storage subsystem having a same volume identification as a source volume. For a command received on the at least one of the plurality of upgraded components, the verify I/O command is invoked on at least one of a comparable one of the plurality of existing components. If the command is verified, the command is driven. The at least one of the plurality of upgraded components disguises a true volume identification of the target volume from the at least one of the plurality of existing components.