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Chapter 2

Introduction to the Properties of a Node

This chapter introduces the roles, qualification levels and attributes of nodes. For information about the types of nodes, see the Netra High Availability Suite Foundation Services 2.1 6/03 Overview.

Membership Roles

Peer nodes can be recognized by the CMM API as having the following membership roles:

Master node

A node with membership role CMM_MASTER. This node coordinates all of the cluster membership information. The master node has the current view of the cluster configuration and all the nodes receive the cluster view from the master node.

Vice-master node

A node with membership role CMM_VICEMASTER. The vice-master node can take over the master role of the cluster. The vice-master node has its own copy of the cluster_nodes_table file. For more information, see the cluster_nodes_table(4) man page.

Out node

Any node configured to be in the cluster that has the membership role CMM_OUT_OF_CLUSTER. This role means that the node is not available for use, for either physical or administrative reasons. Do not distribute tasks on an out node, because it might be undergoing maintenance.

No membership role is assigned to a node running the Foundation Services services and fully participating in cluster communication that is neither a master node nor a vice-master node. Further information about nodes in the cluster is provided by the cluster_nodes_table(4) man page.

For information about the definitions of the roles of nodes in the cluster, see "Cluster Model" in the Netra High Availability Suite Foundation Services 2.1 6/03 Overview.

Membership roles are dynamic and are defined by the master node. Unless the membership role of a node is CMM_OUT_OF_CLUSTER, the node is by default viewed as being in the cluster. While the node has the CMM_OUT_OF_CLUSTER role, the qualification level and CMM_FLAG_SYNCHRO_NEEDED flag are meaningless. Information about the membership role of a node can be found in the sflag field of the cmm_member_t structure. See Using the sflag Field of the cmm_member_t Structure.

Qualification Levels

The qualification level of a node is applicable only to master-eligible nodes. On these nodes, the qualification level determines whether the node can participate in an election for the master role or vice-master role. A master-eligible node can be qualified or disqualified. The qualification levels of a master-eligible node are:

CMM_QUALIFIED_MEMBER

The node is qualified to be master. Only meaningful for eligible nodes.

CMM_DISQUALIFIED_MEMBER

The node is disqualified from being master. Only meaningful for eligible nodes.

For master-eligible nodes, the qualification level is stored in the minimum configuration file, target.conf, on the node and in the cluster node table. For more information, see the target.conf(4) man page. The qualification level is persistent, that is, if the node is rebooted, the node starts with the same qualification level it had before the reboot. The qualification level of a node can be changed during runtime. Diskless and dataless nodes are never assigned qualification levels.

To assign a new qualification level to a node, use the cmm_member_setqualif function. For more information, see the cmm_member_setqualif(3CMM) man page.

An example in which this function is used to trigger a failover in the cluster is provided in this book. See Triggering a Failover by Using the cmm_member_setqualif()Function.

Administrative Attributes

The CMM API recognizes each node in the cluster as having an administrative attribute. An attribute can be any of the following:

CMM_ELIGIBLE_MEMBER

The node is a member of the cluster. The node is a master-eligible node, therefore it is diskfull and can participate in a master or vice-master election.

CMM_FLAG_DISQUALIFIED

The node is part of the cluster and is master-eligible, but this node cannot participate currently in master elections. This flag applies only to master-eligible nodes.

CMM_FLAG_SYNCHRO_NEEDED

The master node disk and vice-master node disk must be synchronized so that the vice-master node can take over the role of master node if necessary. If the disks are not synchronized, the vice-master node cannot become the master node. If the CMM_FLAG_SYNCHRO_NEEDED flag is set, the vice-master node disk is not up-to-date. When the master node disk and vice-master node disks are synchronized, the flag is cleared. The flag applies only to master-eligible nodes, and must not be set by applications.

For more information about Reliable NFS, see the Netra High Availability Suite Foundation Services 2.1 6/03 Overview.

A master node can be demoted because of a change in its administrative attributes, when the vice-master detects a problem on the master, or after a call to the cmm_mastership_release() function. The master node can also be demoted in the case of a failover. See Failover Notifications. A node assumes the master role if it is sufficiently qualified.

Information about the administrative attributes of a node can be found in the sflag field of the cmm_member_t structure. For more information, see Using the sflag Field of the cmm_member_t Structure.

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