1. An overlay network, comprising: a first level-1 cluster of local area networks (LANs); a second level-1 cluster of LANs; wherein: each LAN includes one or more physical computerized nodes each operative to perform data processing and storage operations; a distance between any pair of LANs of the first level-1 cluster of LANs is less than or equal to a predefined level-1 maximum distance value according to a distance metric, and a distance between any pair of LANs of the second level-1 cluster of LANs is less than or equal to the predefined level-1 maximum distance value; one LAN of the first level-1 cluster of LANs has a first cluster medoid node used for measuring distance to other clusters, and one LAN of the second level-1 cluster of LANs has a second cluster medoid node using for measuring distance to other clusters; and a level-2 cluster of LANs formed by the first and second level-1 clusters of LANs, a distance between the first cluster medoid node and the second cluster medoid node in the level-2 cluster of LANs being less than or equal to a predefined level-2 maximum distance value according to the distance metric, the predefined level-2 maximum distance value being greater than the predefined level-1 maximum distance value.