Veritas Cluster Server (VCS)

Chapter 1:Introducing Veritas Cluster Server

Veritas Cluster Server by Symantec is a high-availability solution for cluster configurations. Veritas Cluster Server (VCS) monitors systems and application services, and restarts services when hardware or software fails.

• A single VCS cluster consists of multiple systems that are connected in various combinations to shared storage devices.
• When a system is part of a VCS cluster, it is a node. VCS monitors and controls applications running in the cluster on nodes.
• Applications can continue to operate with little or no downtime.

Figure 1-1 Example of a four-node VCS cluster 

• Client workstations receive service over the public network from applications running on VCS nodes. VCS monitors the nodes and their services.
• VCS nodes in the cluster communicate over a private network.
• VCS runs in a replicated state on each node in the cluster.

About shared storage :

• A VCS hardware configuration typically consists of multiple nodes that are connected to shared storage through I/O channels.
• Shared storage provides multiple systems with an access path to the same data. It also enables VCS to restart applications on alternate nodes when a node fails, which ensures high availability

Figure 1-2 illustrates the flexibility of VCS shared storage configurations.

About LLT and GAB :

VCS uses two components, LLT and GAB, to share data over private networks among systems.

1. LLT (Low Latency Transport) : it's provides fast, kernel-to-kernel communications, and monitors network connections.

LLT configuration files are as follows:

■ /etc/llthosts—lists all the nodes in the cluster

■ /etc/llttab file—describes the local system’s private network links to the other nodes in the cluster

2. GAB (Group Membership and Atomic Broadcast) : It monitors disk communications such as the VCS heartbeat utility.

The /etc/gabtab file is the GAB configuration file.

About network channels for heartbeating :

• For the VCS private network, two network channels must be available to carry heartbeat information.
• Each Linux cluster configuration requires at least two network channels between the systems. The requirement for two channels protects your cluster against network partitioning.

About VCS optional features :

                                                                   1. VCS notifications

2. VCS global clusters 
    
3. I/O fencing

Note : The Veritas Installation Assessment Service (IAS) utility allows the preinstallation evaluation of a configuration, to validate it prior to starting an installation or upgrade.

VCS notifications:

You can configure both SNMP and SMTP notifications for VCS. Symantec recommends you to configure one of these notifications .

• Configure SNMP trap notification of VCS events using the VCS Notifier component
• Configure SMTP email notification of VCS events using the VCS Notifier component

VCS global clusters:

You require a separate license to configure global clusters.

I/O fencing

/O fencing protects the data on shared disks when nodes in a cluster detect a change in the cluster membership that indicates a split brain condition.

About VCS optional components :

Symantec Product Authentication Service

Veritas Cluster Server Management Console

Cluster Manager (Java console)

Figure 1-4 illustrates a sample VCS deployment with the optional components configured.

About Symantec Product Authentication Service (AT) :

VCS uses Symantec Product Authentication Service (AT) to provide secure communication between cluster nodes and clients. It uses digital certificates for authentication and SSL to encrypt communication over the public network to secure communications.

AT uses the following brokers to establish trust relationship between the cluster components:

■ Root broker

A root broker serves as the main registration and certification authority; it has a self-signed certificate and can authenticate other brokers.

■ Authentication brokers

Authentication brokers serve as intermediate registration and certification authorities.

Veritas Cluster Server Management Console :

Veritas Cluster Server Management Console is a high availability management solution that enables monitoring and administering clusters from a single Web console.

Cluster Manager (Java Console) :

Cluster Manager (Java Console) offers complete administration capabilities for your cluster. Use the different views in the Java Console to monitor clusters and VCS objects, including service groups, systems, resources, and resource types.

You can perform many administrative operations using the Java Console. You can also perform these operations using the command line interface or using the Veritas Cluster Server Management Console.