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Method to logically divide the file system into two logical type partitions to reduce non-contiguous allocation of device blocks and improve performance of defragmenter.

IP.com Disclosure Number: IPCOM000173402D
Original Publication Date: 2008-Aug-05
Included in the Prior Art Database: 2008-Aug-05
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Abstract

One of the major roadblocks in achieving a good performance of a file system is the presence of non-contiguous blocks of data in files, a phenomena usually referred to as “fragmentation”. A faster file system not only increases the speed of operations on data files, but also increases the speed of loading and execution of programs. It can be easily shown that most of the fragmentation of the file-system occurs because of the changing size of files. This disclosure proposes a two-fold method to reduce the impact of files that change their sizes on the performance of the file system and to increase the performance of defragmenters. This is achieved by seggregating files that change their length from files that have constant length, together with an attempt to reserve contiguous disk blocks for files as per the specified average or maximum size.

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Method to logically divide the file system into two logical type partitions to reduce non-contiguous allocation of device blocks and improve performance of defragmenter .

Author: Rajbir Bhattacharjee

Proposed a method to decrease fragmentation in a file-system, and to increase the performance of defragmenters by logically partitioning the file-system into two parts, and trying to reserve contiguous disk blocks for files which change their size.

    One of the major roadblocks in achieving a good performance of a file system is the presence of non-contiguous blocks of data in files, a phenomena usually referred to as fragmentation. The allocation of contiguous blocks of data sequentially to files greatly enhances the performance of a file system. The increase in speed is due to the following reasons:
1. Read ahead mechanism of the file system performs better if the blocks of the file are contiguous.
2. Many hard disks maintain an internal cache of disk blocks, and read blocks into the cache in advance.
3. Contiguous disk blocks are located adjacent to each other in the tracks of a disk. The circular motion of the disk and the mechanical momentum of the disk are responsible for better performance if blocks of a file are contiguous.

    A faster file system not only increases the speed of access of data files, but also increases the speed of loading and execution of programs, as (a) the programs themselves reside in the file-system as files, (b) these program read a host of other configuration files and (c) these programs are often paged out into the disk into a file called the page file. Hence if fragmentation can be reduced or prevented, the overall performance of the system will increase.

Files in a file system may be classified into two types:
1. Files that do not change their length (eg. Libraries, executables, etc.), except when there is an upgrade in which the entire file is overwritten.
2. Files that regularly change their size (eg. Data files, configuration files etc.)

    There are a few existing technologies to reduce fragmentation in a file system. The BFS file system attempts to avoid fragmentation. However BFS file systems are limited to boot images, and suffer from the limitation that only regular files are supported. Extents are used by a number of file-systems to reduce fragmentation. However extents lead to sub-optimal usage of hard disk space in case of high disk usage.

    It can be easily shown that most of the fragmentation of the file-system occurs because of the changing size of files.

    This disclosure proposes a two-fold method to (a) reduce the impact of files that change their sizes on the performance of the file system and (b) to increase the

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performance of defregmenters, while avoiding the drawbacks of existing technologies like BFS and extents. The salient points of this two fold method are
1. Separation of the file-system partition into two logical part...