RMAN> Backup database;

Starting backup at 22-DEC-09
using channel ORA_DISK_1
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00001 name=E:\ORACLE\ORADATA\ORCL\SYSTEM01.DBF
input datafile fno=00003 name=E:\ORACLE\ORADATA\ORCL\SYSAUX01.DBF
input datafile fno=00002 name=E:\ORACLE\ORADATA\ORCL\UNDOTBS01.DBF
input datafile fno=00005 name=E:\ORACLE\ORADATA\ORCL\MYUSER.DBF
input datafile fno=00008 name=E:\ORACLE\ORADATA\ORCL\ORCL.DBF
input datafile fno=00004 name=E:\ORACLE\ORADATA\ORCL\USERS01.DBF
input datafile fno=00007 name=E:\ORACLE\ORADATA\ORCL\RMANBAK.DBF
input datafile fno=00006 name=E:\ORACLE\ORADATA\ORCL\BACKUSER.DBF
channel ORA_DISK_1: starting piece 1 at 22-DEC-09
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on ORA_DISK_1 channel at 12/22/2009 17:34:45
ORA-19809: limit exceeded for recovery files
ORA-19804: cannot reclaim 52428800 bytes disk space from 2147483648 limit

备份数据库时出现上述错误，通过更改恢复目标空间大小解决；
SQL> alter system set db_recovery_file_dest_size=4G scope=both;

System altered.