Method for transferring storage data of a virtual machine to be migrated from a first host device to a second host device via a communication network, including: running the virtual machine on the first host device; storing, on a local storage device of the first host device, a disk image used by the virtual machine; detecting, while the virtual machine is running on the first host device, any changes made to the disk image used by the virtual machine; establishing a connection over the communication network from the first host device to the second host device; transferring, to the second host device while the virtual machine is running on the first host device, the disk image used by the virtual machine and the detected any changes made; modifying the disk image transferred to the second host device in response to the detected any changes transferred to the second host device; and starting, using the modified disk image, a migrated virtual machine on the second host device at a current state of the virtual machine running on the first host device.