The current state of a running domain is saved in a file on the disk. Xend restores the state of the domain by using this file. This is similar in concept to the hibernation feature of a laptop. During hibernating, a laptop saves an image of the disk state and shuts itself. To come out of the hibernation, it uses the saved disk image to restore the running state.
In this section we will learn how to save an active domain to a file that can later be used to restore the file to the active state either on the same server or on a different Xen server. You must ensure that you have enough disk space to save the image files before you try to save a domain to an image file.