Basically there are two ways to create ASM diskgroup

• Manual (sqlplus)
• Automatic (ASMCA)

Check for available candidate disks

ASMCMD> lsdsk -p --candidate
Group_Num  Disk_Num      Incarn  Mount_Stat  Header_Stat  Mode_Stat  State   Path
        0         0           0  CLOSED      PROVISIONED  ONLINE     NORMAL  /dev/oracleasm/disks/DATA
        0         2           0  CLOSED      PROVISIONED  ONLINE     NORMAL  /dev/oracleasm/disks/RECO
        0         1           0  CLOSED      PROVISIONED  ONLINE     NORMAL  /dev/oracleasm/disks/REDO

Check for permissions on disks

[root@dgprim01 grid]# ls -lHL /dev/oracleasm/disks/
total 0
brw-rw----. 1 oracle oinstall 8, 33 Sep  2 20:04 DATA
brw-rw----. 1 oracle oinstall 8, 65 Sep  3 00:41 OCRVOD
brw-rw----. 1 oracle oinstall 8, 49 Sep  2 20:04 RECO
brw-rw----. 1 oracle oinstall 8, 81 Sep  2 20:04 REDO

Check for asm disks and their status

SQL> select NAME,GROUP_NUMBER,DISK_NUMBER,MOUNT_STATUS,HEADER_STATUS,PATH from v$asm_disk;

NAME                 GROUP_NUMBER DISK_NUMBER MOUNT_S HEADER_STATU PATH
-------------------- ------------ ----------- ------- ------------ --------------------
                                0           0 CLOSED  PROVISIONED  /dev/oracleasm/disks
                                                                   /DATA

                                0           1 CLOSED  PROVISIONED  /dev/oracleasm/disks
                                                                   /REDO

                                0           2 CLOSED  PROVISIONED  /dev/oracleasm/disks
                                                                   /RECO

OCRVOD_0000                     1           0 CACHED  MEMBER       /dev/oracleasm/disks
                                                                   /OCRVOD

Create the diskgroups DATA and RECO by manual method using sqlplus

SQL> create diskgroup DATA external redundancy disk '/dev/oracleasm/disks/DATA';

Diskgroup created.

SQL> create diskgroup RECO external redundancy disk '/dev/oracleasm/disks/RECO';

Diskgroup created.

Create diskgroup using ASMCA as well (this step is optional as i show method of creating diskgroup only for redo diskgroup using ASMCA). Click on create

Give diskgroup name ,choose the available disk and click ok

Post the step, the diskgroup get created