Get the information about ASM disks:
SELECT GROUP_NUMBER, DISK_NUMBER, TOTAL_MB/1024 GB, NAME FROM v$asm_disk;
Get the information about ASM diskgroups (including used space and the free space):
SELECT GROUP_NUMBER, NAME, TOTAL_MB/1024 TOTAL_GB, FREE_MB/1024 FREE_GB FROM v$asm_diskgroup;
