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

By: Walter Metcalf

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  • JFS Utilities

    In addition to the parameters of the IFS statement, LVM also provides a set of utilities. WARNING: Some of these utilities can be hazardous to your data if used incorrectly. For safety's sake, back up your data before using them.

    Here is a list of the JFS utilities, and a brief description of each.

    1. CHKDSK

      1. When used on a JFS drive, CHKDSK accepts the additional parameter "/B" (without quotes) which causes bad block processing. Unlike other CHKDSK parameters, "/B" is used when the file system is active, makes bad blocks permanently unavailable, thereby removing them from the LVM fixed length bad block list.

    2. FORMAT

      1. When used on a JFS drive, FORMAT accepts the following additional parameters:

        1. /BS:n, where n is the block size in bytes to use for the file system.

        2. /LS:n, where n specifies the size of the journaling log to create in megabytes. The default is 0.4% of the file system size.

        3. /S, which specifies the file system created should support sparse files. The default is dense files.1

    3. DEFRAGFS [/Q] drive

      1. As its name implies, this utility defragments a JFS's volume's free space. "Q" indicates "query" and, if specified, returns the drive's current status, and performs no defragmentation activities.

    4. EXTENDFS [/LS:] drive

      1. This utility is used after a volume has been enlarged using LVM to adjust the JFS file system to fit the volume. The optional /LS parameter indicates the size of the journal log to be created. The system will automatically perform a reboot if one is required.


      1. Undocumented. This utility queries the settings of the cache, and can be used to set its lazy write parameters.


      1. Undocumented. Diagnostic tool that shows a formatted log of the last CHKDSK process.
This completes our look at the Journaling File System. I hope you have found it profitable.

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Walter Metcalf

For Further Reading:

Inside OS/2 Warp Server for e-business, Chapter 4; IBM Redbook SG24-5393-00 Very complete and detailed treatment of all aspects of LVM as used in WSeB.

A Short Introduction to LVM and JFS.
Brief overview of both JFS and LVM as used in eComStation, and a fairly detailed treatment of JFS.


1 According to Inside OS/2 Warp Server for e-business by IBM, p. 130: 'When formatted sparse JFS does not allocate physical disk space to hold byte ranges of a file that has never been written to.'

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