Conversion of a JFS to JFS2 filesystem

Answer

No, a JFS filesystem cannot be converted to become a JFS2 filesystem.

The two types of filesystems have completely different structures and inode allocation methods. There are three recognized methods to move data from a JFS to a JFS2 filesystem.

1. Copy With Parallel Filesystems

If you have the space, creating a second filesystem and simply copying the data is the easiest way.
# crfs -v jfs2 -g myvg -a size=20G -A yes -m /newfilesystem
This will create a 20GB filesystem in volume group "myvg" with mount point "/newfilesystem".

Mount the filesystem:
# mount /newfilesystem

Copy the data from your existing filesystem to it, with a command similar to:
# cd /mydata; pax -x pax -w * | (cd /newfilesystem; pax -v -r )
(Using pax will preserve sparseness that may exist in database files. See technote T1000145 "About Sparse Files" for more information on this topic)

Unmount the current filesystem and rename it:
# unmount /mydata
# chfs -m /oldfilesystem /mydata

Rename the mount point of the new filesystem and mount it::
# chfs -m /mydata /newfilesystem
# mount /mydata

At this point test your application or check over your data. If all is well remove the old filesystem:
# rmfs /oldfilesystem

2. Backup and Recreate

Back up your data on the original filesystem, remove it and recreate as JFS2. Use this when you do not have enough disk space to have the same filesystem existing in parallel.

Back up the data using whatever command you usually use to back up the files.

Unmount and remove the old filesystem:
# umount /mydata
# rmfs /mydata

Create the filesystem again:
# crfs -v jfs2 -g myvg -a size=20G -A yes -m /mydata
# mount /mydata

Restore your data to /mydata

3. Alternate Disk Copy for Rootvg

If your filesystems are rootvg ones, neither of these methods will work. However you can use alt-disk copy to create a new rootvg. Using the -T flag will recreate the filesystems as JFS2:

-T