1) Please backup the database(s) contained inside the associated diskgroup.


2) Then shutdown the databases contained inside the associated diskgroup.


3) Dismount the associated diskgroup to verify no client database connections are accessing this specific diskgroup:

SQL> alter diskgroup <diskgroup> dismount;


4) Resize your physical disk/LUN at OS/hardware level.


5) Mount back the diskgroup:

SQL> alter diskgroup <diskgroup> mount;


6) Then resize the ASM disk as the following example:

 

SQL> ALTER DISKGROUP <diskgroup> RESIZE DISK <disk name> <size>M REBALANCE POWER <1-11>;

SQL> ALTER DISKGROUP DATA RESIZE DISK DISK_A1 SIZE 5000 M REBALANCE POWER 11;