US Patent 10146456 Data storage system with multi-level, scalable metadata structure

A data storage system creates, maintains and utilizes logical storage structures including (1) a pool of device extents on user devices, organized into data portions of mapped RAID groups each having a data portion and a RAID group metadata element having (i) a basic portion and (ii) a mapping portion mapping each set of device extents to logical RAID extents per RAID type, (2) a pool logical device (e.g., an internal mapped RAID) in the pool, storing the mapping portions of the metadata elements of the mapped RAID group, and (3) a system logical device on separate system devices, storing (i) the basic portions of the metadata elements of the RAID groups, and (ii) a pool metadata element including a pool mapping portion for the pool logical device.