result of an incomplete migration. An incomplete migration is
one where the MBR is not turned into a PMBR after creating the
GPT. This early in the game it's more convenient to allow the
inconsistency, because that avoids that we have to destroy the
MBR partitioning for now.
but is useful to have handy. EFI GPT partitions are used instead of the
fdisk+disklabel combination. They are pure 64 bit LBA, are fully
extensible, support up to 16383 partitons per disk, etc.