JFS Version 3

For 10.20, the kernel and the JFS commands now support a new disk layout for JFS file systems called Version 3. The existing Version 2 layout is also supported. This means that file systems of either type can be mounted and all JFS commands work on both versions.

By default, mkfs(1M) creates a Version 3 layout, although there is an option to create a Version 2 layout. There is a new command, vxupgrade(1M), to convert Version 2 file systems to Version 3. The upgrade is performed on-line (that is, while the file system is mounted). You do not have to reboot the system, change any configuration files (such as /etc/fstab), or even unmount the file system. Once a JFS file system has been upgraded to the Version 3 disk layout, the process cannot be reversed.

JFS file systems created during a cold installation will use the new Version 3 layout. However, if an earlier release is updated to HP-UX 10.20, the JFS file systems will still use the Version 2 layout. You can choose to upgrade the pre-existing file systems to Version 3 using the vxupgrade(1M) command.

Note that a Version 3 JFS file system cannot be mounted by an earlier release of HP-UX. Therefore, under some circumstances, you might prefer to create a new JFS file system with the older Version 2 layout.

Several features of HP-UX 10.20 are supported on JFS only with the new Version 3 layout. These include large files and large UIDs (see the sections "Large Files" and "Large User IDs" in this chapter for details). It is not possible to create large files or files owned by users with large UIDs on a Version 2 JFS file system.

HP-UX 10.20 also supports the new Data Management API defined by the Data Management Interface Group (DMIG), but only on JFS file systems using the Version 3 disk layout. The DMAPI is not supported on Version 2 JFS file systems or on HFS file systems.

Impact

The JFS Version 3 disk layout will not affect any existing applications. The kernel and commands continue to support all JFS interfaces that were supported in past releases of HP-UX. Applications should not rely on the file system's internal data structures. If they do, applications might not work correctly.

Compatibility

For 10.20, JFS is source-compatible and binary-compatible with earlier releases of HP-UX. This is true whether the new Version 3 disk layout or the older Version 2 disk layout is used.

Alternatives

As in the past, you can create either HFS or JFS file systems and can freely mix the two on a single computer. If you create JFS file systems, you now have the choice of using the Version 2 or the Version 3 disk layout. These versions can also be freely mixed.