The purpose of the CIM is to allow applications to determine when it is safe to perform operations on shared resources. It is safe to perform operations on shared resources when a node is a member of a cluster that is in a consistent state.
A consistent state is means that all the nodes of a cluster that are members of the CIM set are in a known and safe state. The nodes that are members of the CIM set are specified in the CIM configuration. Only these nodes are considered when the CIM determines the state of the cluster. When a node first joins or forms a cluster, the CIM indicates that the cluster is consistent only if it can determine the status of the other nodes that make up the CIM set and that those nodes are in a safe state.
As methods for guaranteeing a quorum, PRIMECLUSTER supports the following three CIM methods:
Node State Management (NSM) method
MMB method
The NSM method uses the state of the other node as reported by CF and periodically determines whether that node is in a known state. If the state is known, The CF states that are determined as known are UP and DOWN. If the node is being activated or is in LEFTCLUSTER state, that state is determined to be unknown (a quorum is not guaranteed).
The MMB method uses the PRIMEQUEST MMB interface and asynchronously determines the state of a cluster node.
In this way, the CIM provides applications with a set of functions that determine nodes are in a consistent state (whether or not there is a quorum).
PRIMECLUSTER uses CIM to determine whether a user application process that uses resources shared by multiple nodes in a cluster can be processed safely without triggering process contention. In other words, it is safe to perform operations on shared resources if the node executing the process is a member of a cluster system that is in a consistent state (quorum). In the PRIMECLUSTER system, the consistent state is set when all the nodes in the cluster system monitored by the CIM are either in operating (UP) or stopped (DOWN) state and are also in a safe state. The nodes monitored by the CIM to all the nodes that were set when the CIM was configured. Only these nodes are considered when the CIM checks the cluster status. When a node first joins or forms a cluster, the CIM indicates that the cluster is consistent only it can determine the status of the other nodes that make up the CIM set and that those nodes are in a safe state.
CIM currently supports the Node State Management (NSM) method. The CIM reports on a cluster state that a node state is known and safe (True), or a node state is unknown (False) for the node. True and False are defined as follows:
True - All CIM nodes in the cluster are in a known and safe state.
False - One or more CIM nodes in the cluster are in an unknown or unsafe state.
