Duplicating Databases
                 (source: Oracle Docs)

Duplicating a Database to a Remote Host by Using Active Database Duplication with Image Copies

There are multiple questions to answer as prerequisities.

a. Do backups of the source database exist?

If the database backups do NOT exist, then

1. The principal advantage of active database duplication is that it does not require source database backups. 
2. One disadvantage of this technique is the negative performance effect on the network. 
3. Another disadvantage is that the source database is running processes required to transfer the files to the auxiliary host, thereby affecting the source database and production workload.

If the database backups exist, then

1. If the source database backups exist, and 
   if the effect on the network is unacceptable, then 

backup-based duplication may be a better option. 

You can copy backups to temporary storage and transfer them manually to the destination host. 

If duplication is made with a connection to the target or the recovery catalog, then 
the backup files on the destination host must have the same file specification as they had on the source host. 

Otherwise, this is not a requirement.

b. Is a recovery catalog available?

If a recovery catalog exists, then you can perform backup-based duplication without connecting RMAN as TARGET to the source database. This technique is advantageous where network connections from the auxiliary host to the source database are restricted or prone to intermittent disruptions. When you perform duplication without using a target connection, the source database is unaffected by the duplication.

c. How much disk space is available on the destination host?

When you perform duplication by using disk backups, disk space on the destination host can be an issue. 

For example, 

if the source database is 1 terabyte (TB), and if you duplicate the database from disk backups without using shared disk or network file system (NFS), then 

you must have at least 2 terabytes (TB) of space available on the destination host. In some environments, manual transfer of backups is necessary because NFS performance is a bottleneck.

d. Are the source and destination hosts connected by a LAN or a WAN?

Performance of active database duplication is probably slower on a wide area network (WAN) than on a local area network (LAN). If the performance degradation on a WAN is unacceptable, then backup-based duplication may be the only viable option.

e. When do you plan to duplicate the database?

If you must duplicate the database during a period of high user activity, then the loss of network throughput caused by active duplication may be a problem, making backup-based duplication a better choice. Also, in active database duplication, the RMAN channels that are required for copying files to the auxiliary host can affect performance.

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1. Ensure that the prerequisites for the selected duplication technique are met.
   The prerequisites depend on the type of database duplication being performed. 
   Some prerequisites are common to all types of duplication and others are specific to a particular type of duplication.
2. Complete the required planning tasks before you begin database duplication.