Quote Originally Posted by gopu_g
When you place a tablespace in backup mode, the Oracle instance notes that a backup is being performed and internally compensates for it. As you know, it is impossible to make an authentic copy of a database file that is being written to. On receipt of the command to begin the backup, however, Oracle ceases to make direct changes to the database file. It uses a complex combination of rollback segments, buffers, redo logs, and archive logs to store the data until the end backup command is received and the database files are brought back in sync.
Gopu
err not true, the datafile DO get written to, that is so horribly wrong.

All that happens is that the datafile headers get frozen.

Stop writing rubbish