To get a the UUID of a disk, do
$ sudo blkid /dev/sdb1 /dev/sdb1: UUID="a48cf280-fcc7-4283-ab31-5a23440bd2fa" TYPE="ext4"
Now you can refer to the device as /dev/disk-by-uuid/xxx. Or you
can mount by UUID from fstab as follows:
UUID=a48cf280-fcc7-4283-ab31-5a23440bd2fa /external ext4 rw,user,noauto
)