When I began to work in my current company there were 3 databases working on a RAC environment formed by two nodes. There were many reboots due to misconfiguration (one for all... they didn't use a gigabit switch for private interconnection, but.. a CROSS cable!!!!): I pretended to move some instances to new machines and now we have three RAC installations.
The following are the steps to disable two of the previous three instances from automatic startup.
I issued the following command to check the status of these databases:
srvctl status database -d SID -v
I shutted down both databases with immediate option:
srvctl stop database -d SID -o immediate
Again I looked at the status:
Then I definetely disabled the automatic startup of those databases with the following command:
srvctl disable database -d SID