Comment 0 for bug 1569289

'root-tar' (indicating a root filesystem in tar archive format) as been used for full system containers in OpenStack both under the libvirt/lxc driver and under the new lxd driver (nova-lxd package).

Users are working around the lack of 'root-tar' default support in glance by uploading images in this format as 'raw' (which is incorrect) or updating the list of supported disk formats using the glance-api configuration file.