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This research paper will present research on various file systems available for Linux. I will discuss the main features of each file system before making the final comparison and drawing a conclusion.

Extracts from this document...

Introduction

A Comparison of Linux File Systems

CB353

Co-operative Operating Systems

Assignment 1

By

Christopher Waite

Student Number: - 0103396

Abstract

This research paper will present research on various file systems available for Linux. I will discuss the main features of each file system before making the final comparison and drawing a conclusion.

Introduction

A file system is used by an operating system to organize and access files.  This document will examine the various ‘built-in’ and independent file systems available for Linux.  This will cover file systems suitable for both personal and enterprise use. I will go into depth about the functions offered by each file system and the advantages and disadvantages of its use in the Linux environment.

In Linux a file system doesn’t talk directly to the kernel, instead the Linux kernel contains a VFS (Virtual file system) layer. This isn’t a complete file system but instead it is an integral part pf the kernel. Card, Ts’o and Tweedie go on to explain that the virtual file system layer calls specific actions in the actual file system when requested to do so. It is designed to make it easier to migrate a file system into the Linux kernel.

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The diagram demonstrates that when the user invokes a process such as deleting a file, this process is trapped by the system, which then calls the VFS layer. The VFS calls the appropriate command in the file system in use on that partition. This command is then stored in the buffer where the appropriate device drivers are used to access the disk.

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Middle

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The diagram demonstrates how the File allocation table works. The Doc1 file in the directory points to the first block in the FAT. This block in turn points to another block. This continues until the last block of the file. The last block has a special entry to identify it as the end of the file.

Ext2FS

Ext2FS an abbreviation of extended file system version 2.  This was the standard file system before its replacement came in the form of Ext3FS. The core features used in Ext2FS still remain in its successor. Appleton (1997, p. 2) explains that the Ext2 file system is broken up into groups. Each group contains a superblock, a group descriptor, a block bitmap, an I-node bitmap, an I-node table, and data blocks. These are set when the partition is formatted and cannot be altered. Information general to the whole file system is stored in the superblock. This is important as the file system is mounted using this information. The superblock in each group contains a copy of the original in case of an error. If an error occurs then the system can recover the original from one of the copies.

The second extended file system also implements I-nodes. Each file on the disk is associated with one I-node. An I-node contains information on the file such as its creation date and time, its permission, and pointers to the files location on disk. The most important feature of an I-node is the pointers it contains. This principal is detailed by Appleton (1997, p.3) who tells us that an I-node has 15 pointers.

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Conclusion

Conclusion

Whilst I have not covered all of the file systems, I have covered the ‘main-stream’ file systems available for Linux.  Linux is an operating system that is available in many ‘flavours’. It is intended to be tailored towards individual users by offering an unprecedented amount of flexibility. This flexibility also reaches to the file system. All of the file systems I have reviewed for Linux are based on a group of people ideas as to how a file system should operate. Linux is about finding a file system that suits your needs. Ext3FS is clearly holding onto its predecessor’s features too much and without the adoption of new techniques file systems like XFS and ReiserFS will quickly become take its place as standard for the home user. For the time being however, Ext3FS is still the preferred file system for home users. It offers enough support for large drives to be viable and its journal capabilities enable it to recover quickly from crashes.

References

http://e2fsprogs.sourceforge.net/ext2intro.html, 29 October 2003

Appleton, R. (1997). ‘A Non-Technical Look Inside the EXT2 File System’. Linux Gazette (no. 21), 2-3.

Florido, J. L. S. (2000). ‘Journal File Systems’. Linux Gazette (no. 55), 2-10.

http://www.ntfs.com/fat-allocation.htm, 2 November 2003

Best, S. (2002). ‘JFS for Linux’, Free Software Magazine (Feb 2002 issue)

http://www.namesys.com, 30 October 2003

Bibliography

Ellis, S. and Raithel, J. (1994). ‘Getting Started with XFS Filesystems’. Silicon Graphics (Doc No. 007-2549-001)

http://support.microsoft.com/default.aspx?scid=http://support.microsoft.com:80/support/kb/articles/q154/9/97.asp&NoWebContent=1, 2 November 2003

http://www.easydesksoftware.com/fat.htm, 26 October 2003

Muller, G. (1999). ‘A Visual Introduction to Linux’, Philips Research (version 2.2)

Christopher Waite         7th November 2003

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