Move a datafile online

Command

ALTER DATABASE MOVE DATAFILE
  '/u01/oradata/ORCL/customer_data01.dbf'
  TO '/u03/oradata/ORCL/customer_data01.dbf';

-- Move into ASM:
ALTER DATABASE MOVE DATAFILE
  '/u01/oradata/ORCL/customer_data01.dbf' TO '+DATA';

-- Use KEEP to retain the old file instead of deleting it:
-- ALTER DATABASE MOVE DATAFILE '...' TO '...' KEEP;

What it does

Moves a datafile to a new location while the database is open (12c+); changes storage without downtime.

When to use it

When changing the disk/mount point, migrating to ASM, or moving to hot storage.

Caution

Requires 12c or later and Enterprise Edition. The move generates extra I/O. If you do not use KEEP, the old file is deleted.