man mkfs:
-U UUID Set the universally unique identifier (UUID) of the filesystem to UUID. The format of the UUID is a series of hex digits sepa‐ rated by hyphens, like this: "c1b9d5a2-f162-11cf-9ece-0020afc76f16". The UUID parameter may also be one of the following: clear clear the filesystem UUID random generate a new randomly-generated UUID time generate a new time-based UUID