A boot restore system and associated processes for rapidly restoring virtual machine images are described. The boot restore system can boot a virtual machine from a set of one or more backup files in a backup repository. The boot restore system can make the backup set available for use by the virtual machine immediately or otherwise rapidly. Thus, users may not have to wait for an actual virtual disk image to be copied to a separate file system before accessing the restored backup set. While a user is accessing the virtual machine, a live migration process can migrate the backup set to a target file system, without any disruption or substantial disruption in use of the running virtual machine.