In the past it was not possible to shrink a JFS. Has that changed in the meantime, is somebody working on it, is it planned ...?

How would it be possible to replace JFS with another FS without having to backup and restore the files?

3 Answers 3


It's not possible to shrink a JFS file system using the standard tools. Compunix provides some tools that claim to be able to shrink JFS filesystems, but there's no widespread account of their reliability or success rates.

It's generally not possible to switch filesystems in-place, unless you're changing versions of the same filesystem (ext2->ext3->ext4) or converting FAT to NTFS on certain Windows systems.

In theory, if your JFS file system doesn't take up the whole disk, and you're very lucky about where the FS is placed on the disk, you could copy files to another partition, then delete the JFS partition and grow the other partition and its filesystem (be sure to pick something that can grow, like ReiserFS or XFS).

  • I think the idea about creating a second partition, dumping the files and then growing the new partition is a good bet. I've done this myself when dual booting Windows and Linux. I had to grow my Linux partition (XFS) but it was at the end of the drive. So I shrank my Windows partition, created a second XFS partition between the two existing partitions, dumped the files over and grew the new partition back over the old one. Worked great. And was very easy.
    – baudtack
    Commented May 22, 2009 at 23:37
  • keep in mind that the direction of resize wasn't relevant on AIX long before, it's a limitation of the linux port. The only FS that works well with that regard on Linux is VxFS. Commented Aug 14, 2023 at 12:53

According to this post it's only possible to shrink JFS2.

Sadly, I don't think you can migrate from JFS to JFS2 online.

  • Linux JFS is based on AIX JFS2. (I didn't figure that out for years either). But the tooling/kernel work is missing. Commented Aug 14, 2023 at 12:53

If you have backups in place, you could give it a shot and try convertfs - it does something similar to the suggestion from "yesterday", but in small steps and automated. (But then again, if you have backups - isn't it easier to just recreate the fs and restore? :)

In theory it should work. (I have actually used it with success...once)

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