Veritas File System 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

The VERITAS File System
Online System Administration
Chapter 110
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.
File System 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.Use the vxresize command
when resizing both the volume and the file system. The vxresize command guarantees that the file system
will shrink or grow along with the volume. Do not use the vxassist and fsadm_vxfs commands for this
purpose. Refer to the VERITAS Volume Manager Administrators Guide for additional information about
such capabilities.