As we head towards exascale storage, there is a necessity to scale up existing storage media such as HDDs and NAND SSDs. Scaling NAND flash involves reducing feature size and packing more bits in each cell, as well as stacking more cells in a 3D space. With Quad-Level Cell (QLC) NAND, and its 4 bits/cell the limitations of this approach become apparent. QLC has drastically reduced write endurance (10% of TLC), significantly reduced write throughput (15% of TLC), and reduced read throughput (40% of that of TLC). If QLC is utilized in the same performance tier as current NAND flash, it will wear out much faster negating the cost benefits of capacity gains. We demonstrate novel techniques of data placement, migration, and garbage collection to ameliorate the effect on performance and cost by QLC SSDs.

We look at different techniques to combine heterogeneous media, such as TLC NAND, QLC NAND, Optane SSDs, in a way which extends the lifetime of the system and improves read performance. While all of these devices occupy the same performance tier in traditional storage tiering, there is a need for newer management techniques given the varying properties of these devices. The superior endurance and in-place updates on the Optane, the expanded capacity, but lower endurance of QLC, and the all-round properties of TLC NAND can be combined to create an efficient data store which minimizes wear on QLC and boosts read throughput. Utilizing the NVMe Zoned Namespaces (ZNS) offers us greater control over data placement and garbage collection in SSDs. We demonstrate our techniques in a userspace data management system.