Exploiting non-volatile RAM to enhance flash file system performance

Abstract

Non-volatile RAM (NVRAM) such as PRAM (Phase-change RAM), FeRAM (Ferroelectric RAM), and MRAM (Magnetoresistive RAM) has characteristics of both non-volatile storage and random access memory (RAM). These forms of NVRAM are currently being developed by major semiconductor companies and are expected to be an everyday component in the near future. The advent of NVRAM may possibly bring about drastic changes to the system software landscape. In this work, we develop a new Flash memory based file system that exploits NVRAM in order to improve system performance. Specifically, we discuss the initial design and implementation of a file system that stores all metadata in NVRAM, while storing all file data in Flash memory. In so doing, we make two contributions in this work. First, we present a model that analyzes the amount of NVRAM that is needed for specific Flash memory storage capacity. Experimentally, we verify that this model represents the exact NVRAM usage in the realistic environment. Second, we present quantitative experimental results that show how much performance gains are possible by exploiting NVRAM. Compared to YAFFS, a popular Flash memory based file system, we show that this file system requires only minimal time for mounting and that the execution time improves by a maximum of 600% and an average of 437% for the realistic workloads that we considered. Copyright 2007 ACM.