Lifespan Analysis for Redundant Array of Independent Module Based Solid State Drives

Solid state drives (SSD) are usually built using a NAND flash memory array. An SSD controller manages datastreams stripped to multiple flash memory channels. The device could be regarded as a level-0 structure of redundant array of independent disk (RAID), the technical term for a disk array system. This typical SSD controller architecture is called an intrinsic RAID (iRAID). An iRAID-based SSD controller has to execute sophisticated wear-leveling algorithms and dynamically calculate the lifespan of each flash memory chip as well as run error correction coding. redundant array of independent module (RAIM) was proposed to simplify the SSD controller by applying a group of standardized memory modules instead of raw flash memory chips. One of the widely recognized memory modules is the embedded multi-media card (eMMC) module, which is a small component, typically with a ball grid array package, and is found in consumer applications. In the paper, we have described the methods needed to optimize wear-leveling in an array of eMMC modules and deduced a formula to evaluate and optimize the lifespan of an RAIM-based SSD. A silicon SSD controller was implemented to verify the analysis. The positive result revealed that the lifespan of the RAIM-based SSD could be improved in consumer-grade eMMC modules.