User manged Recovery After the Loss of Datafile

Losing Datafiles Whenever you are in NoArchivelog Mode:
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If you are in noarchivelog mode and you loss any datafile then whether it is temporary or permanent media failure, the database will automatically shut down. If failure is temporary then correct the underline hardware and start the database. Usually crash recovery will perform recovery of the committed transaction of the database from online redo log files. If you have permanent media failure then restore a whole database from a good backup. How to restore a database in archivelog is discussed on
http://arjudba.blogspot.com/2008/05/recovering-database-in-noarchivelog.html.

Losing Datafiles Whenever you are in Archivelog Mode:
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If the datafile that is lost is under SYSTEM tablespace or if it is a datafile contain active undo segments then database shuts down. If the failure is temporary then correct the underline hardware and start the database. Usually crash recovery will perform recovery of the committed transaction of the database from online redo log files.

If the datafile that is lost in not under SYSTEM tablespace and not contain active undo segments then the affected datafile is gone to offline. The database remains open. In order to fix the problem take the affected tablespace offline and then recover the tablespace.