A system for managing storage of data units includes a data storage system configured to store multiple data blocks, at least some of the data blocks containing multiple data units, and configured to store, for at least some of the data blocks, corresponding historical information about prior removal of one or more data units from that data block, the removal affecting at least some addresses of data units in that data block. The system is configured to perform at least one operation that accesses at least a first data unit stored in a first data block according to address information interpreted based on any stored historical information corresponding to the first data block.