Paper Title: QLC and Mixed Mode SSDs Require Deep FTL-Tuning

Paper Abstract: QLC NAND supports a new level of flexibility as its cells can be written as QLC (4 bit, with 16 values per cell), favoring capacity over performance, or programmed using more traditional storage modes (TLC, MLC, SLC or a mix thereof) each of which emphasize distinct characteristics of NAND. This allows us to dynamically rebalance the storage allocation between capacity, performance and endurance, potentially in any mix suitable for specific applications. This additional degree of freedom enables new potential applications, from HDD+SSD replacements with "mixed-mode SSDs" to applications tuned for SSDs, to multiple levels of caching and data availability as demanded by new application models. However, this ductility comes at a cost as mixed capabilities require complex management metrics. Many of these management requirements are extremely challenging, to the point some of them can only be accomplished by fine tuning the Flash Translation Layer (FTL) to align with the internal architecture of the NAND. The challenges include error correction codes, failure and recovery domains, asymmetry management and the continuous run-time tuning of the FTL and NAND operating parameters. The presentation will cover some of the key innovative configurations QLC will allow and what type of technology and deep FTL-NAND tuning will be necessary to support the next generation of SSDs. By the end, the audience will appreciate the new range of solutions they will be able to deploy, along with the significant level of care required to insure they develop a solid solution.

Paper Author: Karl Schuh, Senior Firmware Architecture Manager, Micron

Author Bio: Karl Schuh has over 30 years of experience in the storage industry, with a focus on device firmware. He currently leads Micron’s SSD Firmware Architecture Team. Prior to Micron, Karl led firmware SDD architecture and design teams at SandForce and LSI.