1. A method of collaborative storage management, the method comprising: in a non-volatile hierarchical storage system including multiple controllers each controlling at least one of a plurality of storage units of physical storage within the hierarchical storage system, each of the plurality of storage units including at least one memory device, a first controller among the multiple controllers receiving health reports from at least second and third controllers among the multiple controllers regarding health of multiple storage units of physical storage under control of the second and third controllers, wherein the at least one storage unit under control of the second controller includes at least one different memory device than the at least one storage unit under control of the third controller; the first controller maintaining a health database of information received in a plurality of health reports including the health reports; in response to a health event and based on information in the health database, the first controller modifying logical-to-physical address mappings of one or more of multiple storage units under its control such that data having greater access heat is mapped to relatively healthier storage units and data having less access heat is mapped to relatively less healthy storage units; and thereafter, the first controller directing write requests to storage units under its control in accordance with the modified logical-to-physical address mappings.