High Availability Clustering

High Availability Clustering

Charter: Provide Dell’s customers with the appropriate high-availability solution: testing, validating, certifying, and sustaining Dell’s MSCS-based HA cluster products/solutions and cultivating knowledge and providing collateral around mainstream cluster-aware applications.


For many businesses, computing systems have become such an integral part of their company's business that severe consequences can occur when their systems are unavailable. These systems are used for critical business functions such as order processing and tracking, inventory control, transaction processing, customer support, and electronic commerce. And when these critical functions are not accessible it can result in lost revenue, lost productivity, reduced customer satisfaction, possible data loss or reduced decision making capabilities. As a result, in today's global environment, these computing systems must be available 24 hours per day, 365 days per year.

Improved availability must balance the cost of downtime against the cost of any proposed solution to find the most cost-effective method of availability. The first consideration should be the basic quality and reliability of the server (to minimize failures). Dell servers have been designed with a broad array of redundant features to maximize a server's availability. High Availability Clusters provide the next level of availability to further increase business critical applications availability.

Dell's strategy is to provide clustered solutions that are built with industry standard commodity based components, which deliver entry level, mid-range and high-end availability solutions. The entry level, mid-range and high-end cluster have all been designed to remove all single points of failure. Each cluster level provides the ability to recover from additional failures, thus protecting against many multiple component failures. By removing failure points, higher levels of availability can be achieved. Thus, customers can now use the same build to order model they have become accustomed to with Dell servers, to build the availability level that best meets their high availability requirements.

High Availability Clustering
Figure 1: Microsoft Cluster Server (MSCS)

Microsoft Cluster Server (MSCS) controls access to the storage system(s). Although both servers have physical connections to the storage system(s), only one server can have access to the data on any disk at any point of time

The systems that are clustered together are interconnected via a private LAN and utilize this LAN for a heartbeat mechanism to determine the health of each system. When a failure occurs, the failed system's applications and application data is migrated to and restarted on the healthy system. The effort required to restart the application varies greatly depending on the type of application (e.g., file/print vs. DBMS) and the amount of data associated with the application. Ideally, when an application switches from one node to another, the user experiences no disruption at all and isn't even aware that the job has been switched to a different server.

Realistically, the disruption the user experiences can range from a slight delay to an extensive application restart. By transferring the users to a backup system, high availability clustering is designed to minimize the amount of downtime.

Article ID: SLN310228

Last Date Modified: 09/17/2020 04:50 PM

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