VERITAS File SystemÖ 3.5 (HP OnlineJFS/JFS3.5) AdministratorÆs Guide (December 2002)

Chapter 1

The VERITAS File System

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.