The present invention provides techniques for assignment and layout of redundant data in data storage system. In one aspect, the data storage system stores a number M of replicas of the data. Nodes that have sufficient resources available to accommodate a requirement of data to be assigned to the system are identified. When the number of nodes is greater than M, the data is assigned to M randomly selected nodes from among those identified. The data to be assigned may include a group of data segments and when the number of nodes is less than M, the group is divided to form a group of data segments having a reduced requirement. Nodes are then identified that have sufficient resources available to accommodate the reduced requirement. In other aspects, techniques are providing for adding a new storage device node to a data storage system having a plurality of existing storage device nodes and for removing data from a storage device node in such a data storage system.