The present disclosure relates to a data storage system, and processes and computer programs for such data storage system, for example including processing of: managing one or more metadata tree structures for storing data to one or more storage devices of the data storage system in units of blocks, each metadata tree structure including a root node pointing directly and/or indirectly to blocks, and a leaf tree level having one or more direct nodes pointing to blocks, and optionally including one or more intermediate tree levels having one or more indirect nodes pointing to indirect nodes and/or direct nodes of the respective metadata tree structure; maintaining the root node and/or nodes of at least one tree level of each of at least one metadata structure in a cache memory; and managing I/O access to data based on the one or more metadata structures, including obtaining the root node and/or nodes of the at least one tree level of the metadata structure maintained in the cache memory from the cache memory and obtaining at least one node of another tree level of the metadata structure from the one or more storage devices.