Online System Administration

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:

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.