VERITAS File System 3.5 (HP OnlineJFS/JFS 3.5) Administrator's Guide (August 2003)

Chapter 1
The VERITAS File System
Online System Administration
22
Online System Administration
A VxFS file system can be defragmented and resized while it remains online and accessible to users. The
following sections provide an overview of these features.
Defragmentation
Free resources are initially aligned and allocated to files in the most efficient order possible to provide
optimal performance. On an active file system, the original order of free resources is lost over time as files
are created, removed, and resized. The file system is spread further and further along the disk, leaving
unused gaps or fragments between areas that are in use. This process is also known as fragmentation and
leads to degraded performance because the file system has fewer options when assigning a file to an
extent (a group of contiguous data blocks).
VxFS provides the online administration utility fsadm to resolve the problem of fragmentation. The fsadm
utility defragments a mounted file system by:
• Removing unused space from directories.
• Making all small files contiguous.
• Consolidating free blocks for file system use.
This utility can run on demand and should be scheduled regularly as a cron job.
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.
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 VxFS utility fsadm can expand or shrink a file
system without unmounting the file system or interrupting user productivity. However, to expand a file
system, the underlying device on which it is mounted must be expandable.
VxVM facilitates expansion using virtual disks that can be increased in size while in use. The VxFS and
VxVM packages complement each other to provide online expansion capability. Refer to the VERITAS
Volume Manager Administrator’s Guide for additional information about such capabilities.