"ORA-15040: diskgroup is incomplete” while Mounting or Dropping disk group

I faced the below error while trying to mount the disk group. Got the same error while trying to drop this disk group.

ORA-15032: not all alterations performed
ORA-15017: diskgroup "DATA" cannot be mounted
ORA-15040: diskgroup is incomplete

Just to give the background, this is two node RAC cluster and the servers had been reimaged to upgrade the OS. I have built Oracle cluster after server re-imaging.

Then I started ASMCA to create the new ASM disk groups and noticed that the disk group “DATA” was already present in “Dismounted” state as shown in below screenshot.

Now I was suspecting that this issue could be due to some residue remaining in some disks after server re-imaging. It could be possible, if somehow few disks have been missed to format after re-imaging the servers.

Executed below query to find the disks which was causing the issue.

SQL> select GROUP_NUMBER, name, disk_number, MOUNT_STATUS, HEADER_STATUS, MODE_STATUS, state, os_mb, total_mb, path from v$asm_disk where HEADER_STATUS not in ('CANDIDATE', 'PROVISIONED', 'FORMER') order by GROUP_NUMBER,name;

The output of above query showed three disks with:

“HEADER_STATUS” as “MEMBER”,

“GROUP_NUMBER” as “0”

It means that there are three disks associated with the disk group “DATA” which is in dismounted status as shown in screenshot.

Formatted these three disks using “dd” command. Re-opened ASMCA and the disk group “DATA” got disappeared. Then created the disk group “DATA”.

Hope this blog will be helpful if you come across this scenario where servers have been re-imaged for cluster build and missed to format some or all disks in the cluster after server re-imaging.