VERITAS Storage Foundation 4.1 Oracle Administrator's Guide

Understanding Fragmentation Prerelease 8 September 2005, 8:54am
76 VERITAS Storage Foundation for Oracle Administrator’s Guide
Understanding Fragmentation
When free resources are initially allocated to files in a VERITAS file system, they are aligned in the
most efficient order possible to provide optimal performance. 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.
Controlling 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.