A method for maintaining a mapping structure for maintaining metadata for snapshots in a virtualized storage environment, includes taking a snapshot of a virtual disk, generating an entry in a metadata structure for the snapshot, wherein the entry includes metadata for blocks in the snapshot that have been modified since a preceding snapshot and lazily generating an entry in the mapping structure for the snapshot, wherein the entry includes values for each block in the snapshot, wherein a value for a block indicates a presence of metadata in the metadata structure for the block or an absence of metadata in the metadata structure for the block.