Oracle RAC Background Processes!!

The following are the additional processes spawned for supporting the multi-instance coordination and can be thus called Oracle Real Application cluster background processes(RAC).
DIAG - (Diagnosability Daemon) this process would be responsible for Monitoring the health of the instance and capture the data for instance process failures.
LCKx - This process manages the global enqueue requests and the cross-instance broadcast.  In case of multiple Global Cache Service Processes (LMSx) , one would find that the Workload is automatically shared and balanced.
LMON - provided services are also known as cluster group services (CGS) and LMON particularly handles the recovery associated with globl resources.LMON called as Global Enqueue Service Monitor, monitors the entire cluster to manage the global enqueues and the resources. It is responsible to manage instance and process failures and the associated recovery for the Global Cache Service (GCS) and Global Enqueue Service (GES).
LMDx - Full form is Global Enqueue Service Daemon.It is the lock agent process that manages enqueue manager service requests for Global Cache Service enqueues to control access to global enqueues and resources. The LMD process also handles deadlock detection and remote enqueue requests.These requests are originating from another instance.
LMSx - The Global Cache Service Processes are the processes that handle remote Global Cache Service (GCS) messages. Up to 10 Global Cache Service Processes can be there. The number of the processes varies depending on the amount of messaging traffic among nodes in the cluster. The LMSx handles the acquisition interrupt and blocking interrupt requests from the remote instances for Global Cache Service resources. For cross-instance consistent read requests, the LMSx will create a consistent read version of the block and send it to the requesting instance. The LMSx also controls the flow of messages to remote instances.
It handles the blocking interrupts from the remote instance for the global cache service resources by managing the resource requests & cross-instance call operations for the shared resources.
It is also responsible for building a list of invalid lock elements and validating the lock elements during recovery. It does the Handling of the  global lock deadlock detection and Monitoring for the lock conversion timeouts
To read in bullet form refer:
 http://vibhork.blogspot.com/2010/10/understanding-real-application-cluster.html