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Energy-Aware Reorganization in Log-Structured File Systems

Energy-Aware Reorganization in Log-Structured File Systems
Subject:Power Management

Dr. Andreas Weißel, Prof. Dr. Frank Bellosa, Prof. Dr. Wolfgang Schröder-Preikschat

Graduand:Philipp Janda


As mobile computing devices become more and more popular, the corresponding hardware and applications become more complex, comfortable, and thus energy hungry. Since the main advantage of mobile devices is their ability to work without a stationary power supply an important challenge has been to reduce power consumption, thereby prolonging the uptime of the devices in battery mode.

One way to reduce the energy needs of a mobile device is the adoption of a special data layout on its storage devices, which accounts for the mechanical mode of operation of a hard disk. Such a special data layout is, for example, a log-structured file system. The major disadvantage of a log-structured file system is that it wastes storage space during operation in order to reduce energy consumption.

To reclaim the wasted space, a particular free space management is necessary. While there are multiple possibilities with different advantages and disadvantages, all methods involve some overhead and an increased energy consumption. The question is whether the addition of such a free space manager will negate the energy efficiency of a log-structured file system and thus make log-structured file systems unsuitable for saving energy.

This work analyzes the properties of different free space management techniques and gives recommendations for their application in log-structured file systems. Implementations of variants of a certain class of free space management are described and tested for performance and energy consumption. Measurements of the cleaning processes were performed for different fragmentations and in comparison to other file systems. Although the two tested prototypes are similar, they show vast performance differences under certain circumstances.


  author = {Philipp Janda},
  title = {Energy-Aware Reorganization in Log-Structured File Systems},
  type = {Study Thesis},
  address = {Operating System Group, University of Erlangen, Germany},
  month = apr # "~5",
  year = 2005,
  url = {http://www4.informatik.uni-erlangen.de/SA/pdf/SA-I4-2005-03-Janda.pdf}