When circular logging is disabled, log files accumulate on the transaction log disk drive until an online normal (full) or incremental backup is performed. During an online backup operation, the following occurs:
The backup process copies the specified database files.
Patch files are created as required (patch files maintain transactions written during a backup operation to the portion of an .edb file that has already been backed up).
Log files created during the backup process are copied to tape.
Patch files are written to tape.
Log files older than the checkpoint at the start of the backup operation are purged. These files are not required because the transactions have already been committed to the .edb files and the .edb files have been written to tape.