From the KnowledgeBase
How do I exclude certain files or folders from being backed up?
An include-exclude list contains statements that identify any specific files you want to include or exclude from backup services. This list is contained in the dsm.opt file.
For example, you might want to exclude all swap files, cache folders, easily reproducible files (such as object files), or operating system files. You can enter broad statements in the dsm.opt file that exclude entire groups of files. Then, you can enter include statements to make exceptions to those broad statements.
The dsm.opt file provided at installation time contains an include-exclude list. You should use this list as a minimum even if you do not want to add anything to it. If no include-exclude list exists in the options file, TSM considers all files for backup services and uses the default management class for backup and archive services.