Data migration with write back to source with data pre-copy

A non-transitory computer readable medium containing software that migrates data from a first storage device to a second storage device that are both coupled to a host computer, the software comprising:

• executable code that causes data of the first storage device to start being copied from the first storage device to the second storage device;
• executable code that causes the host computer to transition from performing I/O operations with the first storage device to performing I/O operations with the second storage device by modifying metadata used for I/O operations to change a mapping of logical devices to physical devices only after causing data of the first storage device to start being copied from the first storage device to the second storage device and before completion of the copying;
• executable code that migrates data from the first storage device to the second storage device independently of any I/O operations by the host;
• and
• executable code that acknowledges a data write operation from the host only after the data has been successfully written to both the first storage device and the second storage device, wherein the data is written by the host to the second storage device only and the data is copied from the second storage device to the first storage device and wherein other data from a portion of a same area of the first storage device is copied from the first storage device to the second storage device prior to the host writing the data to the second storage device.