oracle 无法mount..在线等

ARC1: Failed to archive thread 1 sequence 5559 (19809)
Wed Feb 8 14:44:44 2012
Errors in file /u01/app/oracle/admin/risemail/bdump/risemail_arc0_5983.trc:
ORA-19815: WARNING: db_recovery_file_dest_size of 21474836480 bytes is 100.00% used, and has 0 remaining bytes available.
Wed Feb 8 14:44:44 2012
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You have following choices to free up space from flash recovery area:
1. Consider changing RMAN RETENTION POLICY. If you are using Data Guard,
then consider changing RMAN ARCHIVELOG DELETION POLICY.
2. Back up files to tertiary device such as tape using RMAN
BACKUP RECOVERY AREA command.
3. Add disk space and increase db_recovery_file_dest_size parameter to
reflect the new space.
4. Delete unnecessary files using RMAN DELETE command. If an operating
system command was used to delete files, then use RMAN CROSSCHECK and
DELETE EXPIRED commands.
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ARC0: Failed to archive thread 1 sequence 5558 (19809)