Impact of NVRAM write cache for file system metadata on I/O performance in embedded systems

ABSTRACT

File systems make use of part of DRAM as the buffer cache to enhance its performance in traditional systems. In this paper, we consider the use of Non-Volatile RAM (NVRAM) as a write cache for metadata of the file system in embedded systems. NVRAM is a state-of-the-art memory that provides characteristics of both non-volatility and random byte addressability. By making NVRAM a write cache for dirty metadata, we retain the same integrity of a file system that always synchronously writes its metadata to storage, while at the same time improving file system performance to the level of a file system that always writes asynchronously. To show quantitative results, we develop an embedded board with NVRAM and modify the VFAT file system provided in Linux 2.6.21 to accommodate the NVRAM write cache. The experimental results show that substantial reductions in execution time are possible from an application viewpoint. Another consequence of the write cache is its benefits at the FTL layer, leading to improved wear leveling of Flash memory and increased energy savings, which are important measures in embedded systems.

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INDEX TERMS

Primary Classification:
  C. Computer Systems Organization
  C.3 SPECIAL-PURPOSE AND APPLICATION-BASED SYSTEMS
      Subjects: Real-time and embedded systems

Additional Classification:
  D. Software
  D.4 OPERATING SYSTEMS
      D.4.3 File Systems Management
          Subjects: Directory structures; Access methods

General Terms:
Design, Experimentation, Measurement, Performance

Keywords:
Non-Volatile RAM (NVRAM), file system, flash memory, flash translation layer (FTL), metadata