Oracle ASM Disk Group Not Mounted in DBCA

Step 1: Check ASM Instance Status

Login as grid user:

su - grid

Check ASM instance:

ps -ef | grep pmon

You should see something like:

asm_pmon_+ASM1

If ASM is not running, start it:

sqlplus / as sysasm

Then:

startup;

Step 2: Verify ASM Disk Groups

Connect to ASM:

sqlplus / as sysasm

Check disk groups:

select name,state,type,total_mb,free_mb from v$asm_diskgroup;

If the state shows:

DISMOUNTED

then the disk group must be mounted manually.

Step 3: Mount ASM Disk Group

Run:

alter diskgroup DATA mount;

If you also have FRA:

alter diskgroup FRA mount;

Now verify again:

select name,state from v$asm_diskgroup;

Expected output:

DATA   MOUNTED
FRA    MOUNTED

Step 4: Check ASM Disks

Verify ASM disks:

select path,header_status,mount_status from v$asm_disk;

Healthy disks should show:

• HEADER_STATUS → MEMBER or CANDIDATE
• MOUNT_STATUS → CACHED

Step 5: Restart DBCA

After mounting the disk groups:

1. Close DBCA
2. Reopen DBCA
3. Select:
   • Automatic Storage Management (ASM)
4. Click Browse

Now the ASM disk groups should appear properly.

Common Reasons for ASM Disk Group Not Mounted

1. ASM Instance Not Started

ASM background processes are not running.

2. Incorrect ASM Disk Permissions

Oracle/grid user does not have permission on ASM disks.

Check permissions:

ls -l /dev/oracleasm/disks/

3. Oracle ASM Library Driver Not Configured

Verify ASM disks:

oracleasm listdisks

Scan disks again:

oracleasm scandisks

4. Disk Group Dismounted After Reboot

Sometimes ASM disk groups do not auto-mount after system restart.

Useful Commands for ASM Troubleshooting

Check ASM Parameters

show parameter asm_diskstring;

Discover ASM Disks

select path from v$asm_disk;

Mount All Disk Groups

alter diskgroup all mount;

Conclusion

If ASM disk groups are not visible in Oracle DBCA, the issue is usually related to dismounted ASM disks or inactive ASM instances. By checking ASM status and mounting the disk groups manually, the issue can be resolved quickly.

This is one of the most common Oracle 19c ASM installation issues faced during RAC and standalone database setup. Proper ASM configuration ensures smooth database creation and storage management.