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Cluster Server Technology Keeps Your Application Running When the Critical Server Fails

When an organization is dependable to the computer resources infrastructure and downtime is not acceptable to the business production, deployment of fault tolerant Server technology such as Clustering is a must for the businesses today. If the servers are down, the business stops. Therefore, such server clustering technology is solutions that must be adopted to keep the business run if one of the critical servers fails.

Clustering

Clustering is one of server fault tolerant technologies offered by Windows server 2003 (and later) which is dedicated to run one or more applications by configuring two or more application servers in such a way to provide fault tolerance and load balancing. If one server fails to operate, the other server will take over the role to keep the application operational. This is the concept of fault tolerance in server clustering technology.

In a server cluster technology, each of the servers runs the same critical applications. When one of the servers fails, the other server will take over the role automatically. This is the "failover" concept. If the failed server is back to normal, other server nodes will recognize this condition and the clustering system will use the server again. This is a "failback" concept.

Server Clustering Technology

In Windows server 2003 and later, there are two types of fault tolerance server technology: Server Cluster and Network Load Balancing (NLB). The difference between the two technologies lies on the types of applications that must be run by the servers and also the types and characteristic of the data they use.

Network Load Balancing (NLB)

Network Load Balancing (NLB) is one of the server redundancy offered by Microsoft which is easy to install, manage, and maintain. You can use the available hardware and software in the servers, no need of additional software or hardware. You can use the application available in Windows 2003 "Network load balancing manager" to create, manage, and monitor the NLBs. NLB mostly run the memory stateless applications, the applications which data is not changed all the time.

Characteristic:

• Supported by all types of Windows 2003 including Standard, Enterprise, and Datacenter types Server
• Can be used to deploy up to 32 nodes Network Load Balancing where each of the server has duplicate copy of the application that you want to provide to the users.
• Full load balancing for both TCP and UDP traffic
• Can be used for Web servers, ISA servers, VPNs, Media servers, and Terminal Servers

Network load balancing works by creating such a virtual network adapter on each of the nodes that represents a single cluster entity. Virtual adapter has independent IP address and MAC address different from each of the IP addresses given to each server interfaces. Clients will access the virtual IP address instead of accessing each of the server nodes.

If a request comes from a client to the cluster IP address, all the nodes in the cluster system will receive and process the message. In each of the nodes in NLB cluster, an NLB service will function as the filter between the cluster adapter and the computer TCP/IP stack. This filter will allow the NLB for the calculation in deciding which node in the cluster system will be responsible to response to the client's request. Each of the nodes in the cluster does not need to make communication between them. Each of the nodes will make the same independent calculation and make their own decision whether to respond the client's request or not. The calculation formula will only be changed if the number of server nodes changes.

Server Cluster

The other types of fault tolerance Server technology is Server Cluster which is designed for applications which data is huge enough and changed frequently and is typically called statefull Applications and contain databases such as Microsoft SQL, Exchange server, server file and printers. All of the nodes in the cluster system are connected to a set of data and share a single SCSI bus or SAN (storage area network). All nodes have the same access to the same application and each node can also process the client request every time. You can configure each of the nodes to be active or passive. The active node can receive client requests, while the passive node is idle and function as the "failback" when the active node is failure.

• Similar to the NLB, server cluster also has the independent name and IP address separate from each of the nodes IP addresses. It is therefore when the active node fails to function, clients do not need to know what's going on to the system. Clients still access the same name and the same IP address because the system will be soon back to normal using the standby machine. If there are many servers in X node clustering, the survival node will take over the failed server.
• Server cluster can only operate under Windows server 2003 Enterprise edition and Datacenter edition. Windows server 2003 Standard edition can only work for NLB but not cluster.
• Up to maximum 8 server nodes to function as failover and failback each. Failback is not configured by default; you should configure it manually or automatically.
• Server Cluster requires special disk drive such as Fiber Channel, Shared SCSI, or SAN. Fiber Channel is a high speed up to 100 Mbps serial networking technology using full-duplex communication. But SCSI uses parallel signal technology.
• Typically used for SQL databases, MS Exchange, File and Print server etc.

X Node Clustering

In X node clustering you can create minimum 2 nodes and up to maximum 8 node failover / failback clustering. For example in X node cluster system, you can deploy 4 server nodes where each server is active and also function as the survival node from the designated server when the server is failure. Each of the nodes has direct access to the share storage. Each of the servers has primary role and the designated survival role. Each of the servers has special connection link via a dedicated network connection which is used to detect the heart beat for all the four nodes. Each of the nodes can detect if there is a failure of the node and the designated node will take over the role function.

By Ki Grinsing

About the Author

Ki Grinsing was graduated from a technical college with the additions of MCSE and CCNA certifications and long years of working experiences in IT. For complete article please visit: Server cluster redundancy and Computer networking hardware

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