Online and quiescent backups
You can create a backup while the database server is online or in quiescent mode. The terminal you use to initiate the backup command is dedicated to the backup (displaying messages) until the backup completes. Once you start a backup, the database server must remain in the same mode until the backup finishes; changing the mode terminates the backup activity.
Online backup
You can use an online backup when you want your database server accessible while you create the backup.
Some minor inconveniences can occur during online backups. An online backup can slow checkpoint activity, and that can contribute to a loss in performance. However, this decline in performance is far less costly than the time that you lose when users were denied access to the database server during a backup.
During an online backup, allocation of some disk pages in storage spaces can temporarily freeze. Disk-page allocation is blocked for one chunk at a time until you back up the used pages in the chunk.
Quiescent backup
You create a quiescent backup while the database server is quiescent. Use quiescent backups when you want to eliminate partial transactions in a backup.
Do not use quiescent backups when users need continuous access to the databases.