1. An object storage system comprising: a server adapted to communicate with users of the object storage system over a network; a plurality of data storage devices which store and retrieve data objects of the users and which are arranged into a plurality of locations; a storage controller circuit associated with each location to direct data transfers between the associated data storage devices and the server using an existing map structure stored in a first memory that describes the data objects in each location, the existing map structure comprising a list of devices corresponding to the data storage devices, a partition assignment list to map partitions of data objects to the devices, and a partition shift hash; and a management circuit adapted to generate a new map structure in a second memory, migrate at least one data object from a first location described by the existing map structure to a second location described by the new map structure, and to distribute the new map structure to each of the storage controller circuits responsive to a data migration complete signal indicating successful completion of the migration of the at least one data object so that no additional migrations are necessary to conform the data objects in each location to the new map structure.