Improving Performance of Linux File System with Adaptive File Rearrangement

• Main Authors: Kai-Yu Cheng, 鄭凱宇
• Other Authors: 姜美玲
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/07169594855789745110

碩士 === 國立暨南國際大學 === 資訊管理學系 === 96 === Many computer devices are innovated continuously with the evolution of the technology. For example, the speed of CPU is accelerated, the access speed of RAM is increased, and the capacity of storage is getting larger and larger. However, hard disk is still the bottleneck of the system performance. The data access time of the hard disk includes seek time, rotational latency, and transfer time. Among them, seek time still wastes most of the total access time. When the data is stored discontinuously in the disk, the disk head needs to move more distances in order to access the data. The increased moving distances of the disk head not only increases the disk seek time but also decreases disk transfer rate. In this thesis, we will focus on how to store hot data in the central cylinders of the disk and dynamically determine whether the cold data should be moved into the central cylinders of the disk, when it has been accessed frequently. This can improve the disk layout and decrease the seek time of accessing in the hard disk. In our research, we store hot files (i.e frequently accessed files) in the Reserved Area located at the center of the hard disk by modifying Linux Ext3 file system. Because the access frequencies of hot files are higher, the disk head will access files inside the Reserved Area when the system accesses hot files. The purpose is to decrease seek time for accessing hot file in the hard disk by shortening the disk head movement distance to improve the file system performance. Besides, we also propose a method to determine whether the cold file when it becomes hot should be moved to the Reserved Area. When the cold file is accessed frequently, the system will determine the file has become hot. The system will also determine whether the location of file in the hard disk is close to the Reserved Area. If the location of the data is closed to the Reserved Area, the data will not be moved, because the benefit is less than the system overhead of file moving. We have implemented this system by modifying the Ext3 file system of Linux kernel 2.6 and created a performance benchmark to simulate the operation behaviors of the BBS system. The result of experiments shows that the modified Ext3 file system can effectively shorten 11.39-30.14% of the disk access time. Besides, when the cold file becomes hot, the file will be moved to the Reserved Area. If the location of this file is close to the Reserved Area, the system will determine whether the file needs to be moved into the Reserved Area. This method can improve 3.29-18.86% of the system performance.