Veritas Storage Foundation for Oracle 5.0 Administrator's Guide, HP-UX 11i v3, Second Edition, December 2008

On an active file system, the original order is lost over time as files are created,

removed, or resized. As space is allocated and deallocated from files, the available

free space becomes broken into fragments. This means that space must be assigned

to files in smaller and smaller extents. This process is known as fragmentation.

Fragmentation leads to degraded performance and availability. The degree of

fragmentation depends on file system usage and activity.

How to control fragmentation

VxFS provides online reporting and optimization utilities to enable you to monitor

and defragment a mounted file system. These utilities are accessible through the

file system administration command, fsadm. Using the fsadm command, you can

track and eliminate fragmentation without interrupting user access to the file

system.

Types of fragmentation

VxFS addresses two types of fragmentation:

■ Directory Fragmentation

As files are created and removed, gaps are left in directory inodes. This is

known as directory fragmentation. Directory fragmentation causes directory

lookups to become slower.

■ Extent Fragmentation

As files are created and removed, the free extent map for an allocation unit

changes from having one large free area to having many smaller free areas.

Extent fragmentation occurs when files cannot be allocated in contiguous

chunks and more extents must be referenced to access a file. In a case of

extreme fragmentation, a file system may have free space that cannot be

allocated.

How to monitor fragmentation

You can monitor fragmentation in VxFS by running reports that describe

fragmentation levels. Use the fsadm command to run reports on directory

fragmentation and extent fragmentation. The df command, which reports on file

system free space, also provides information useful in monitoring fragmentation.