The fastest method of moving data is to copy the database data files to the target database without interpreting or altering the data. With this method, Data Pump Export is used to unload only structural information (metadata) into the dump file. This method is used in the following situations:
The TRANSPORT_TABLESPACES parameter is used to specify a transportable tablespace export. Only metadata for the specified tablespaces is exported.
The TRANSPORTABLE=ALWAYS parameter is supplied on a table mode export (specified with the TABLES parameter) or a full mode export (specified with the FULL parameter) or a full mode network import (specified with the FULL and NETWORK_LINK parameters).
When an export operation uses data file copying, the corresponding import job always also uses data file copying. During the ensuing import operation, both the data files and the export dump file must be loaded.
During transportable imports tablespaces are temporarily made read/write and then set back to read-only. This is new behavior introduced as of Oracle Database 12c Release 1 (12.1.0.2) to improve performance. However, you should be aware that this behavior also causes the SCNs of the import job's data files to change, which can cause issues during future transportable imports of those files.
For example, if a transportable tablespace import fails at any point after the tablespaces have been made read/write (even if they are now read-only again), then the data files become corrupt. They cannot be recovered.
Since transportable jobs are not restartable, the failed job needs to be restarted from the beginning. The corrupt datafiles must be deleted and fresh versions must be copied to the target destination.
When transportable jobs are performed, it is best practice to keep a copy of the data files on the source system until the import job has successfully completed on the target system. If the import job should fail for some reason, you will still have uncorrupted copies of the data files.
When data is moved by using data file copying, there are some limitations regarding character set compatibility between the source and target databases. See Oracle Database Administrator's Guide for details.
If the source platform and the target platform are of different endianness, then you must convert the data being transported so that it is in the format of the target platform. You can use the DBMS_FILE_TRANSFER PL/SQL package or the RMAN CONVERT command to convert the data.
Oracle Database Backup and Recovery Reference for information about the RMAN CONVERT command
Oracle Database Administrator's Guide for a description and example (including how to convert the data) of transporting tablespaces between databases