In this paper, we propose three techniques to improve the performance of YAFFS (Yet Another Flash File System), while enhancing the reliability of the system. Specifically, we first propose to manage metadata and user data separately on segregated blocks. This modification not only leads to the reduction of the mount time but also reduces the garbage collection time. Second, we tailor the wear-leveling to the segregated metadata and user data blocks. That is, worn out blocks between the segregated blocks are swapped, which leads to more evenly worn out blocks increasing the lifetime of the system. Finally, we devise an analytic model to predict the expected garbage collection time. By accurately predicting the garbage collection time, the system can perform garbage collection at more opportune times when the user's perceived performance may not be negatively affected. Performance evaluation results based on real implementations show that our modifications enhance performance and reliability without incurring additional overheads. Specifically, the YAFFS with our proposed techniques outperforms the original YAFFS by six times in terms of mount speed and five times in terms of benchmark performance, while reducing the average erase count of blocks by 14%.

The traditional mobile consumer electronics such as media players and smart phones use two distinct memories, SDRAM and Flash memory. SDRAM is used as main memory since it has characteristic of byte-unit random accessibility while Flash memory as secondary storage due to its characteristic of non-volatility. However, the advent of Storage Class Memory (SCM) that supports both SDRAM and Flash memory characteristics gives an opportunity to design a new system configuration. In this paper, we explore four feasible system configurations, namely RAM-Flash, RAM-SCM, SCM-Flash and SCM-Only. Then, using a real embedded system equipped with FeRAM, a type of SCM, we analyze the tradeoffs between performance and energy efficiency of each configuration. Experimental results have shown that SCM has great potential to reduce energy consumption for all configurations while performance is highly application dependent and might be degraded on the SCM-Flash and SCM-Only configuration.