US Patent 9594583 Lightweight snapshots for virtual disks

A snapshot manager in a virtual machine monitor receives a write request comprising data from a guest operating system of a virtual machine, wherein the write request is directed to a sector of a virtual disk associated with the virtual machine. The snapshot manager writes the data from the guest operating system of the virtual machine to the sector in a base image of the virtual disk, the base image comprising a current version of the virtual disk, wherein the virtual disk comprises the base image and a overlay image, the overlay image comprising a snapshot of the base image at a previous point in time.