For taking cold backup database doesn t need to be in any specific archival mode i.e Archive or Noarchieve. This allows us to perform backups when users are using the database. Please note that when a hot backup is running, much more archive files are generated as compared to normal usage of database. It may full disk space available for archive files. These are general outlines of backup process.
Exports are generally much slower than physical backups and import takes very long too.
This is generally not kept as the only backup method in any backup strategy.