In a lengthy
blog post, Lennart Poettering describes the advantages of using the
unique IDs (UUIDs) and flags from the discoverable partitions
specification to label the entries in a GUID Partition
Table (GPT). That information can be used to tag disk images if a
self-descriptive way, so that external configuration files (such as
/etc/fstab) are not needed to assemble the filesystems for the
running system. Systemd can use this information in a variety of ways,
including for running the image in a container: “If a disk image
follows the Discoverable Partition Specification then systemd-nspawn has
all it needs to just boot it up. Specifically, if you have a GPT disk image
in a file foobar.raw and you want to boot it up in a container, just run
systemd-nspawn -i foobar.raw -b, and that’s it (you can specify a block
device like /dev/sdb too if you like). It becomes easy and natural to
prepare disk images that can be booted either on a physical machine, inside
a virtual machine manager or inside such a container manager: the necessary
meta-information is included in the image, easily accessible before
actually looking into its file systems.“

Source: LWN.net – Poettering: The Wondrous World of Discoverable GPT Disk Images