US Patent 9569518 Efficiently storing and retrieving data and metadata

For efficiently storing and retrieving data and metadata in phases, in a first phase, metadata tokens, which are assigned to metadata-emitting entities, are used for storing the data and the metadata together in a single input/output operation while piggybacking the metadata of least active metadata-emitting entities onto one of the metadata-emitting entities having one of the metadata tokens. In a second phase, the metadata is re-written to a metadata delta journal for reclaiming the metadata tokens. In a third phase, the metadata journal is applied to a metadata structure containing the metadata of the storage system, the metadata delta journal is then cleared after successfully updating the main metadata structure with the metadata of the metadata journal. The metadata journal is swapped with an empty metadata journal for concurrently adding metadata while retaining the metadata journal until applying the metadata delta journal to the metadata structure.