SQL> select name, ALLOCATION_UNIT_SIZE, type from v$asm_diskgroup;

NAME
--------------------------------------------------------------------------------
ALLOCATION_UNIT_SIZE TYPE
-------------------- ------------------
DG_DATA1
             1048576 EXTERN
DG_DATA2
             1048576 EXTERN
DG_DATA3
             1048576 EXTERN
DG_OCR
             1048576 EXTERN


SQL> select file_name, bytes from dba_data_files;

FILE_NAME
--------------------------------------------------------------------------------
     BYTES
----------
+DG_DATA1/crmdb/datafile/users.259.805398403
   5242880

SQL> select GROUP_KFFXP Group#, DISK_KFFXP Disk#, AU_KFFXP AU#, XNUM_KFFXP Extent# 
  2  from X$KFFXP 
  3  where number_kffxp=(select file_number from v$asm_alias where name='&alias_name');
Enter value for alias_name: USERS.259.805398403
old   3: where number_kffxp=(select file_number from v$asm_alias where name='&alias_name')
new   3: where number_kffxp=(select file_number from v$asm_alias where name='USERS.259.805398403')

    GROUP#      DISK#        AU#    EXTENT#
---------- ---------- ---------- ----------
         2          0        441          0
         2          2        444          1
         2          1        441          2
         2          0        442          3
         2          2        445          4
         2          1        442          5