HP JFS 3.3 and HP OnLineJFS 3.3 VERITAS File System 3.3 System Administrator's Guide

Chapter 2 43
Disk Layout
Introduction
other disk layouts, it is generally preferable to use the Version 4 layout
for new file systems.
The vxupgrade command can upgrade an existing Version 3 VxFS file
system to the Version 4 layout while the file system remains online.
vxupgrade can also upgrade a Version 2 file system to the Version 3
layout. See vxupgrade(1M) for details on upgrading VxFS file
systems.You cannot downgrade a file system that has been upgraded.
NOTE You cannot upgrade the root (/) or /usr file systems to Version 4 on an
11.00 system running JFS 3.3. Additionally, we do not advise upgrading
the /var or /opt file systems to Version 4 on an 11.00 system. These core
file systems are crucial for system recovery. The HP-UX 11.00 kernel and
emergency recovery media were built with an older version of JFS that
does not recognize the Version 4 disk layout. If these file systems were
upgraded to Version 4, your system might have errors booting with the
11.00 kernel as delivered, or booting with the emergency recovery media.