Notes on OS/2 Disk Usage III - The Journaled File System (JFS), Concluded

By: Walter Metcalf

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Last week we began a short study of the Journaled File System for OS/2 (JFS) that is shared by Warp Server for e-business (WSeb), the eComStation (eCS) family of products, and the Warp Convenience Packages. In last week's article we summarized the need for a completely new file system, and then gave a brief overview of JFS' main features. In this article we'll conclude the study by showing how it compares with the other operating systems used by OS/2, and then giving JFS a more detailed analysis.

File System Comparison

The best comparison I have found of the various file systems available for OS/2 is in the installation manual supplied with Warp Server for e-business. I have included the chart from this manual below in table form.1

Characteristic Journaled File System (JFS) 386 High Performance File System (386HPFS) High Performance File System (HPFS) FAT File System
Max volume size 2TB (terabytes) 64GB (gigabytes) 64GB (gigabytes) 2GB (gigabytes)
Max file size 2TB (terabytes) 2GB (gigabytes) 2GB (gigabytes) 2GB (gigabytes)
Allows spaces and periods in file names Yes Yes Yes No (8.3 format)
Standard directory and file attributes Within file system Within file system Within file system Within file system
Extended Attributes (64KB text or binary data with keywords) Within file system Within file system Within file system In separate file
Max path length 260 characters 1) 260 characters 260 characters 64 characters
Bootable No 2) Yes Yes Yes
Allows dynamic volume expansion Yes No No No
Scales with SMP Yes No No No
Local security support No Yes No No
Average wasted space per file 256 to 2048 bytes 256 bytes 256 bytes 1/2 cluster (1KB to 16KB)
Allocation information for files Near each file in its i-node Near each file in its FNODE Near each file in its FNODE Centralized near volume beginning
Directory structure Sorted B+tree Sorted B-tree Sorted B-tree, must be searched exhaustively Unsorted linear
Directory location Close to files it contains Near seek center of volume Near seek center of volume Root directory at beginning of volume; others scattered
Write-behind (lazy write) Optional Optional Optional Optional
Maximum cache size Physical memory available Physical memory available 2MB 14MB
Caching program None (parameters set in CONFIG.SYS) CACHE386.EXE CACHE.EXE None (parameters set in CONFIG.SYS)
LAN Server access control lists Within file system Within file system In separate file (NET.ACC) In separate file

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1 Quick Beginnings: Installing OS/2 Warp Server for e-business, by IBM; Part no. ct7s2na; Published in U.S.A.; Table 3. Appendix A, pp 84-85; converted to an HTML table by Michal Necasek in A Short Introduction to LVM and JFS in the November 2000 VOICE Newsletter.

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