Real-Time Access Guarantees for NAND Flash Using Partial Block Cleaning

Increasing use of NAND flash in newer application domains has been possible due to lowering cost per GB, consumer demands for storage and advantages of NAND flash over traditional disks. However, NAND flash has its idiosyncrasies resulting in asymmetric read/write times due to garbage collection and wear leveling requirements. Such asymmetric (non-deterministic) read/write times poses a challenge for the adoption of NAND flash in real-time systems. We present the implementation details of a flash translation layer called GFTL that guarantees strict upper bounds on read/write times that are comparable to a theoretical ideal case. Such guarantees are made possible by dividing the source of non-determinism into deterministic intervals using our proposed approach called partial block cleaning. Using partial block cleaning, the process of garbage collection is divided into several smaller, deterministic steps. Partial block cleaning comes with an overhead of additional space requirements. We provide a proof oil the limit of the additional space requirements.