In Oracle 12c databases, datafile can be moved online. In earlier versions this was not possible. With 12c, a datafile can now be moved from the ASM disk group to the file system or from the file system to the ASM or from the ASM to the ASM.
With the following command, a datafile in the ASM disk group can be moved online to another ASM disk group.
SQL> ALTER DATABASE MOVE DATAFILE '+DATA/ORCL/DATAFILE/data.296.989435351' TO '+DATA2';