col total_size for a10;
col free_size for a20;
select name,total_mb/1024 || 'G' as total_size , free_mb/1024 || 'G' as free_size from v$asm_diskgroup;

或者asmcmd 下 lsdg

步骤：
[oracle@rac6 ~]$ export ORACLE_SID=+ASM1
[oracle@rac6 ~]$ asmcmd
ASMCMD> lsdg
State Type Rebal Unbal Sector Block AU Total_MB Free_MB Req_mir_free_MB Usable_file_MB Offline_disks Name
MOUNTED EXTERN N N 512 4096 1048576 2097152 1486017 0 1486017 0 DATA/
MOUNTED EXTERN N N 512 4096 1048576 1048576 356523 0 356523 0 RECO/