ORA-15041: diskgroup “FRA” space exhausted

The following errors occur in Oracle database alert log :

...
..
.
Unable to create archive log file '+FRA'
Errors in file /u01/app/oracle/diag/rdbms/testdb/TESTDB1/trace/TESTDB1_arc1_12300.trc:
ORA-19816: WARNING: Files may exist in db_recovery_file_dest that are not known to database.
ORA-17502: ksfdcre:4 Failed to create file +FRA
ORA-15041: diskgroup "FRA" space exhausted

CAUSE

Diskgroup FRA had been overallocated, the sum of db_recovery_file_dest_size of all the databases is more than the size of diskgroup FRA.

SQL> select NAME,TOTAL_MB,FREE_MB from v$asm_diskgroup
;

NAME                             TOTAL_MB    FREE_MB
------------------------------ ---------- ----------
...
..
.
FRA                               1024142       120