Global Journal of Computer Science & Technology Volume 11 Issue 6 Version 1.0 April 2011 Type: Double Blind Peer Reviewed International Research Journal Publisher: Global Journals Inc. (USA) Online ISSN: 0975 - 4172 & Print ISSN: 0975-4350 A Quick Review of On-Disk Layout of Some Popular Disk File Systems By Wasim Ahmad Bhat , S. M. K. Quadri Kashmir University Abstract- : Disk file systems are being researched since the inception of first magnetic disk in 1956 by IBM. As such, many good disk file system designs have been drafted and implemented. Every file system design addressed a problem at the time of its development and efficiently mitigated it. The augmented or new designs rectified the flaws in previous designs or provided a new concept in file system design. As such, there are many file systems that have been successfully d in operating systems. Among these designs, some file systems have made an influential impact on the file system design because of their capability to cope up with change in hardware technology and/or user requirements or because of their innovation in file system ign or because time favored them which allowed them to find space in popular operating systems. In this paper, we vide a quick review of on-disk layout of some popular disk file systems across many popular platforms like Windows, Linux & Macintosh. The goal of this paper is to explore the on-disk layout of these file systems to identify the various layout policies and data structures they exploit which made them to be adapted by their native and other operating systems. Keywords: File System, On-Disk, Design, Popular, Review. Classification: GJCST Classification: FOR Code: 100699,100604 A Quick Review of On-Disk Layout of Some Popular Disk File Systems Strictly as per the compliance and regulations of: © 2011 Wasim Ahmad Bhat , S. M. K. Quadri. This is a research/review paper, distributed under the terms of the Creative Commons Attribution-Noncommercial 3.0 Unported License http://creativecommons.org/licenses/by-nc/3.0/), permitting all non- commercial use, distribution, and reproduction inany medium, provided the original work is properly cited. A Quick Review of On-Disk Layout of Some Popular Disk File Systems 2011 Wasim Ahmad Bhatα, S. M. K. QuadriΩ April April Abstract- Disk file systems are being researched since the A File System is a way to organize, store, inception of first magnetic disk in 1956 by IBM. As such, many retrieve, and manage information on a permanent good disk file system designs have been drafted and storage medium such as a disk [4]. File system is an implemented. Every file system design addressed a problem important part of an operating system as it provides a at the time of its development and efficiently mitigated it. The 1 way by which data can be stored, organized, navigated, augmented or new designs rectified the flaws in previous designs or provided a new concept in file system design. As accessed and retrieved in form of files and directories such, there are many file systems that have been successfully from storage sub system. It is generally a kernel module implemented and incorporated in operating systems. Among which consists of algorithms to maintain the logical data these designs, some file systems have made an influential structures residing on the storage subsystems. The impact on the file system design because of their capability to basic key functions that every file system incorporates cope up with change in hardware technology and/or user are basic file operations like copy, move, create, delete requirements or because of their innovation in file system and rename, efficient organization of data for quick design or because time favored them which allowed them to storage and retrieval and efficient use of disk space. find space in popular operating systems. In this paper, we Apart from these basic functions some file systems also provide a quick review of on-disk layout of some popular disk file systems across many popular platforms like Windows, provide additional functions such as compression, Linux & Macintosh. The goal of this paper is to explore the on- encryption, file streams and others. Keeping all the disk layout of these file systems to identify the various layout hardware parameters and workload constant, the policies and data structures they exploit which made them to performance of a hard disk will all depend upon the be adapted by their native and other operating systems. type of file system used. In general file systems were Keywords- File System, On-Disk, Design, Popular, developed in an incremental fashion by individual Review. efforts of researchers and software industry with high cohesion with the hardware limitation and requirements I. INTRODUCTION at that time. Later, refinement of existing file systems [5] ince the advent of computers a mechanism for and new file systems were developed to keep pace with persistent storage of data and/or programs was hardware enhancement and off course need. S needed. On the time line, magnetic disks are the To understand the file system design in general primitive [1] (introduced in 1956 as data storage for an and on-disk layout specifically, we need to review the IBM accounting computer) and still widely used history of its invention a bit so that we can get some secondary storage device. Magnetic disk drive is the overview of the environment and situations in which the most primitive and cost effective storage device. There first file systems were drafted and implemented. has been continuous improvement in its hardware Further, this history will give us some idea about the technology to increase its performance and capacity incremental file system design that has been followed [2]. Although performance has seen less improvement since the inception of first file system. In the early days with respect to capacity, but the tremendous drop in of computers, file systems were simply considered part cost per unit byte, reliability over solid state storage and of the operating system that ran the computer, and in increase in capacity have made disk drives every those days operating systems themselves were rather body’s choice [3]. And hence, disk file systems have new and fancy. One of the first file systems to have a attracted researchers over the globe to exploit its pros name was DEC Tape [6], named after the company that Global Journal of Computer Science and Technology Volume XI Issue VI Version I and minimize its cons. made it (Digital Equipment Corporation) and the physical system the files were stored on (reel-to-reel About α- Research scholar in P. G. Department of Computer Sciences, Kashmir University, India. He did his Bachelor’s degree in Computer tape recorders). The tapes acted like very slow disk Applications from Islamia College of Science & Commerce, India and drives. DEC Tape stored an astoundingly small 184 Master’s degree in Computer Applications from Kashmir University, kilobytes of data per tape on the PDP-8 [7], DEC’s India. popular early minicomputer. It was called a E-mail- [email protected] About Ω - Head, P. G. Department of Computer Sciences, Kashmir minicomputer only because, while the size of a University, India. He did his M. Tech. in Computer Applications from refrigerator, it was still smaller than IBM’s mainframes Indian School of Mines, India and Ph. D. in Computer Sciences from that took up entire rooms. Of course, the invention of Kashmir University. the transistor and integrated circuit allowed another [email protected] ©2011 Global Journals Inc. (US) A Quick Review of On-Disk Layout of Some Popular Disk File Systems whole round of miniaturization. DEC slowly became the day. The introduction of hard disks soon made FAT- extinct while the rest of the world moved to 12 obsolete but file systems got attention and every microcomputers. individual researcher and software industry professional In 1972, Gary Kildall [8] got interested in recognized its importance and started either enhancing working with Microprocessors and got involved with and augmenting the older designs or re-designing 2011 Intel. His research was related to compilers and code some new file systems from scratch. optimization. While working as a consultant in Intel, In this paper, we will look at some most popular April April Kildall developed the Programming file systems’ on-disk layout. The popularity of the file Language/Microprocessor (PL/M) [9] and the Control systems selected is solely based on the popularity of Language/Microprocessor (CP/M) [10]. He wrote CP/M the operating systems that support them natively. The to test out PL/M compiler. CP/M allowed him to store goal of this paper is to look at the layout policies they 2 files and retrieve them from 8-inch floppy. He was able exploit and data structures they use to mitigate the to run and test programs from it, modify them and challenges for which they were designed. In this paper, check their portability by putting floppy in other we will review the native file systems of Windows, Linux machine’s drive. CP/M got very popular because it used and Macintosh operating systems. small amount of memory required to run it, approximately 3 ½ K and had a file system, but it does II. FAT File Systems not have a name. It was very simple, as it stored files in The design of FAT [14] file system is very a completely flat hierarchy with no directories. File simple as it uses simple data structures. This simplicity names were limited to eight characters plus a three- in design has made FAT file system popular and character “extension” that determined the file’s type.