ASM Disk group Free_MB

Hello,

I have an ASM Diskgroup that showing MB not free -

SQL> select NAME, TOTAL_MB, FREE_MB, STATE, TYPE, USABLE_FILE_MB from v$asm_diskgroup

 2 where name = 'MFGP1_FS1'

 3 /

NAME                  TOTAL_MB   FREE_MB STATE      TYPE  USABLE_FILE_MB

-------------------- ---------- ---------- ----------- ------ --------------

MFGP1_FS1              2097148     48960 MOUNTED    EXTERN         48960

But in ASMCMD there are no directories or files

ASMCMD> cd MFGP1_FS1/

ASMCMD> pwd

+MFGP1_FS1

ASMCMD> ls

ASMCMD>

I need drop the Diskgroup to free the disks , but I like to confirm it is not in use.

Any help would be greatly appreciated.