VERITAS File System 4.1 Administrator's Guide

Quality of Storage Service
Customizing QoSS
Chapter 10156
Customizing QoSS
The following information is not essential to QoSS daily operation and management. This
section describes the relationship between the fssweep/fsmove utilities and the allocation
policies and how files and volumes are selected for relocation.
Mapping Relocation Policies to Allocation Policies
The fssweep and fsmove utilities use relocation policies to relocate existing files. Relocation
uses the file system’s allocation policies to determine the current location of each file and to
move files to new locations. Allocation policies also control newly created files. You can
manage allocation policies using the fsapadm utility (see the fsapadm(1M) manual page). In
addition, some allocation policies are automatically managed by the fssweep and fsmove
utilities.
The fssweep and fsmove utilities create allocation policies that have names starting with the
characters fsmove_.
Each component volume has an allocation policy with a name created by appending the
volume name to the string fsmove_. For example, a volume named qoss1a has an allocation
policy named fsmove_qoss1a. The file system also has an allocation policy named
fsmove_ALL that includes all component volumes. VxFS default behavior is to assign
fsmove_ALL to the file system’s mount point as the allocation policy to be used for the newly
created files.
By convention, fssweep and fsmove use volume names, so you need not specify the string
fsmove_ when using these utilities.
The fsmove_ALL allocation policy allows newly created files to reside on any volume. The
order in which volumes are used is by ascending device index numbers. When the fssweep
utility compares a newly created file’s residence against a relocation policy’s list of source
volumes, fssweep treats the files as if they reside on the volume of lowest device index.
When you use the fssweep and fsmove utilities for the first time, the file system can already
contain files that have no allocation policies. The fssweep utility treats such files as though
they reside in the fsmove_ALL allocation policy.
If you use the fssweep and fsmove utilities infrequently, the default allocation policy
allows overflow as each volume becomes full. To the extent that this happens, it becomes
ambiguous where the recently created files really reside.