Merging mapping metadata to promote reference counting efficiency

摘要

A technique for managing metadata in a data storage system designates block pointers as either sources or copies, where sources contribute to reference counts of pointed-to structures but copies do not. The technique maintains parent-child relationships between parent BPSs (block pointer sets) and child BPSs, where each BPS includes an array of block pointers. Each child BPS is created as a copy of a parent BPS and has block pointers initially designated as copies. The technique performs a metadata-merge operation to merge the block pointers of the parent BPS into those of a child BPS by promoting attributes of block pointers in the child BPS from copy to source, avoiding any need to perform reference count updates on structures pointed to by promoted block pointers.