Quick note for people using NFS for shared storage on RAC database. Till RHEL5 we had to ensure nfs,nfslock and portmap service has to be running.
These services are required otherwise you will get following errors while mounting database
ORA-00210: cannot open the specified control file ORA-00202: control file: '/u01/oradata/orcl/control01.ctl' ORA-27086: unable to lock file - already in use
Mostly this could be auto-enabled on boot by using chkconfig command. While working on similar issue today, I found out that this service is not present in RHEL 6
# service portmap status portmap: unrecognized service
The portmap service was used to map RPC program numbers to IP address port number combinations in earlier versions of Red Hat Enterprise Linux.
As per RHEL6 docs, portmap service has been replaced by rpcbind in Red Hat Enterprise Linux 6 to enable IPv6 support.
So following command will work
# service rpcbind status rpcbind (pid 1587) is running...
You can read about NFS and associated processes from RHEL6 docs