If what you need to do is to perform an offline backup of one or more tablespaces, you should first notice that you cannot take the
SYSTEM tablespace or a tablespace with any active
UNDO segments offline. Also, when using this method always take into consideration whether the tablespace is completely self-contained before performing this type of backup, in other words, you should first check if any logical or physical dependencies between objects exist first, for example, if any index related to any table in the tablespace that will become offline is stored in a different tablespace, in such case both the tablespaces (
INDEX) should be taken offline and backed up together.
Never perform offline backups of your database ...