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

Chapter 1 29
The VxFS File System
Online System Administration
Resizing
A file system is assigned a specific size as soon as it is created; the file
system may become too small or too large as changes in file system usage
take place over time.
The HFS file system traditionally offers four solutions to address an
inadequate small file system:
• Move some users to a different file system.
• Move a subdirectory of the file system to a new file system.
• Copy the entire file system to a larger file system.
• Unmount the file system (offline), extend the volume, extend the file
system, then remount the file system.
Most large file systems with too much space try to reclaim the unused
space by off-loading the contents of the file system and rebuilding it to a
preferable size. The HFS file system requires unmounting the file system
and blocking user access during the modification.
When the HP OnLineJFS product is installed, the VxFS utility fsadm
can expand or shrink a file system without unmounting the file systemor
interrupting user productivity. However, to expand a file system, the
underlying device on which it is mounted must be expandable. LVM
facilitates expansion using virtual disks that can be increased in size
while in use. The VxFS and LVM packages complement each other to
provide online expansion capability.
NOTE You can only shrink a file system that uses the version 4 disk layout.
However, even with the version 4 disk layout, it is sometimes not
possible to shrink a file system. When shrinking a version 4 file system,
JFS attempts to move extents off the area of the file system being
reduced. However, if JFS cannot move extents off the area of the file
system being reduced, the shrink will fail.