Applies to: Oracle Server - Enterprise Edition - Version: 10.1.0.2 to 11.1.0.7 - Release: 10.1 to 11.1
From Bug:4465015 [ASM DISKGROUP FOR FLASH RECOVERY AREA DISPLAY MOUNT AND DISMOUNT IN DB ALERT LOG]  (Status: 92,Closed, Not a Bug )

This is expected behavior. The messages you see are not errors (that is why they are prefixed with "SUCCESS"). The database instance is creating and then closing archive logs one at a time in the FLASHDG_NEW disk group. Whenever a database closes its last file in a disk group, it dismounts the disk group. Whenever a database accesses a disk group when it does not have any other files open in the disk group, it mounts the disk group.

If you do not want to see the log messages frequently, you can put a mirrored control-file, or mirrored online redo, or dummy online tablespace data file on the diskgroup. This message will not be output frequently in this case. Because CKPT keeps opening a control-file, LGWR keeps opening an online redo, DBW keeps opening an online tablespace data file. So, the diskgroup is not dismounted until the database shutdown.
Example:
In order to keep the +FRA diskgroup mounted permanently, please create a dummy tablespace on the +FRA diskgroup, which holds the archivelogs, in that way dbw keeps opening an online tablespace data file, so, the diskgroup is not dismounted until the database shutdowns:
SQL> create tablespace dummy_flash datafile '+FRA' size 10M;