Trace File Size

This command can increase the increase the size of trace file to desired value

            alter system set max_dump_file_size='50m'

you can make trace file size unlimited too by using

            alter system set max_dump_file_size='unlimited'

But unlimited size should be used with caution because it may fill you hard drive very fast. For example if you use order organizer and create few sales order with trace on, you would amazed to see size of the trace file