https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/6/html/virtualization_administration_guide/sub-sect-domain_commands-using_blockpull_to_shorten_a_backing_chain
14.5.16. Using blockpull to Shorten a Backing Chain | Virtualization Administration Guide | Red Hat...
14.5.16. Using blockpull to Shorten a Backing Chain | Virtualization Administration Guide | Red Hat Enterprise Linux | 6 | Red Hat Documentation