Does Duplicate Target Database need Pre-existing DB backup?

RMAN 'Duplicate Database' Feature in 11G

You can create a duplicate database using the RMAN duplicate command.
The duplicate database has a different DBID from the source database and functions
entirely independently.Starting from 11g you can do duplicate database in 2 ways.

1. Active database duplication
2. Backup-based duplication

Active database duplication copies the live target database over the network to the
auxiliary destination and then creates the duplicate database.Only difference is that you
don't need to have the pre-existing RMAN backups and copies.

The duplication work is performed by an auxiliary channel.
This channel corresponds to a server session on the auxiliary instance on the auxiliary host.

As part of the duplicating operation, RMAN automates the following steps:

1. Creates a control file for the duplicate database
2. Restarts the auxiliary instance and mounts the duplicate control file
3. Creates the duplicate datafiles and recovers them with incremental backups and archived redo logs.
4. Opens the duplicate database with the RESETLOGS option

For the active database duplication, RMAN does one extra step .i.e. copy the
target database datafiles over the network to the auxiliary instance

A RAC TARGET database can be duplicated as well. The procedure is the same as below.
If the auxiliary instance needs to be a RAC-database as well,
than start the duplicate procedure for to a single instance and convert
the auxiliary to RAC after the duplicate has succeeded.

 If you are using a disk backup solution and duplicate to aremote node you must first copy the backupsets from the original hosts backuplocation to the same mount and path on the remote server.

IO will take place on the remote node and disk backups must be locally available.

本文转自maclean_007 51CTO博客，原文链接:
http://blog.51cto.com/maclean/1278073