Adaptive Object Storage System for Mobile Computing Environments

This paper describes an adaptive object storage system for mobile computing environments. The object storage system adopts the object graph framework[1], and changes the conguration of its structure according to computing environments. The power management has become an important consideration in the design of new hardware and software. The disk is a promising candidate for power management because it is a device with which the user does not interact with directly. With proper management by the operation system, the disk may be spun up and down without the user noticing much dierence in performance or reliability. However, if the portable computers have connected to an AC power supply, spinning down of a disk is not necessary, and performance is more important than energy consumption. On the other hand, if remaining battery is not sucient, the reliability of modied objects becomes more important since the computer may be shutdown at any moment when the battery becomes empty. Therefore, three metrics, performance, reliability, battery consumption should be taken into account for object storage systems in mobile computing environments. When a portable computer is connected to an AC power supply, performance is the most important. However, when the computer is driven by the battery, battery consumption is the most important. On the other hand, if remaining battery is not sucient, reliability is the most important. The adaptive object storage system should take into account the tradeo between the three metrics. Our object storage system is constructed by an object graph that consists of four objects. The object OF is an object that implements the interface of the object storage system and mechanisms for managing objects. The adaptive object MM contains memory management policies that determines which objects should be cached in physical memory. The adaptive object PS contains policies for moving modied objects to the object DM. The adaptive object changes the object processing messages from other objects according to computing environments. The object that currently receives messages is called an active object. Two objects are contained in PS by considering the tradeo between reliability and performance. PS 1 copies objects whenever objects are modied for ensuring the consistency of objects that reside in physical memory and a disk. This policy increases the reliability by sacricing the performance. PS 2 copies objects to a disk periodically for decreasing the number of disk accesses. The object sacrices the reliability for increasing the performance.