jfs_tune

jfs_tune [ -l | -s ] [ -p ] [ -r ] [ -d ] [ -o ]

    The block device (e.g., /dev/sda1) or file containing the JFS filesystem to be tuned.

-l
    Lists the current tunable parameters of the JFS filesystem on the specified device.

-s
    Displays the raw contents of the JFS superblock, primarily for debugging or advanced analysis.

-p
    Makes any specified changes permanent by writing them to the filesystem's superblock. Without this option, changes might only be temporary.

-r
    Sets the maximum number of journal records (transactions) to be written before a commit. A higher value might reduce journal I/O but increase recovery time.

-d
    Sets the maximum journal commit delay in milliseconds. This determines how long data can remain in memory before being committed to the journal.

-o
    Sets specific JFS filesystem options. Examples include barrier to enable I/O barriers for data integrity or nobarrier to disable them for potential performance gains (at increased risk).

jfs_tune is a command-line utility used to examine and modify various tunable parameters of a Journaled File System (JFS). JFS is a robust journaling filesystem originally developed by IBM. This command allows administrators to view current filesystem settings, such as journal record limits (max_recs) and commit delays, and adjust them to optimize performance or behavior for specific workloads. It can persistently write these changes to the filesystem's superblock, ensuring they survive reboots and remounts. Understanding and carefully applying jfs_tune can help in fine-tuning JFS performance, though improper use can lead to instability or data loss. While JFS is less prevalent in modern Linux distributions compared to alternatives like ext4 or XFS, jfs_tune remains essential for managing existing JFS installations.

Using jfs_tune requires root privileges.
Modifying filesystem parameters without proper understanding can lead to filesystem corruption, performance degradation, or data loss. Always back up critical data before making significant changes.
Some changes, particularly those made without the -p option, might not persist across remounts or reboots.
JFS is less commonly used in modern Linux environments compared to more current filesystems like ext4 or XFS.

Changes made with jfs_tune, especially those using the -p option, are written to the filesystem's superblock. For these changes to take full effect, it may be necessary to unmount and then remount the filesystem, although some parameters might be applied immediately on a mounted filesystem.

Tuning parameters like max_recs and delay involves a trade-off between performance and data integrity/recovery time. Larger max_recs or delay values can improve write performance by batching journal operations but might increase the risk of data loss or the time required for filesystem recovery after an unclean shutdown.

JFS (Journaled File System) was originally developed by IBM for its AIX and OS/2 operating systems. It was subsequently ported to Linux, becoming one of the early journaling filesystems available. jfs_tune, as part of the jfsutils package, has been maintained to provide administrators with the ability to fine-tune JFS specific parameters, reflecting the design principles and tunability capabilities inherited from its IBM origins. While its usage has declined on Linux in favor of newer filesystems, it remains a robust utility for environments still utilizing JFS.

jfs_mkfs(8), jfs_fsck(8), mount(8), tune2fs(8), xfs_admin(8)