VERITAS File System 4.1 Administrator's Guide

The VERITAS File System
Online System Administration
Chapter 122
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 Administrator’s Guide for additional information about such capabilities.