Решение cannot backup or copy active file in NOARCHIVELOG mode

[oracle@server ~]$ sqlplus / as sysdba
SQL*Plus: Release - Production on Thu Feb 17 09:51:21 2011
Copyright (c) 1982, 2006, Oracle. All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release - Production
With the Partitioning, OLAP and Data Mining options

SQL> select log_mode from v$database;

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.

SQL> startup mount;
ORACLE instance started.
Total System Global Area 2.0444E+10 bytes
Fixed Size 2191440 bytes
Variable Size 3087011760 bytes
Database Buffers 1.7314E+10 bytes
Redo Buffers 40337408 bytes 

SQL> alter database archivelog;
Database altered.

SQL> alter database open;
Database altered.

SQL> select log_mode from v$database;