SQL Server Cluster: Linking Servers Together for High Uptime using SQL Server

sql server clusterSQL Server is the Relational Database Management System made by Microsoft. As a RDBMS software product, its main purpose is to store data in a database and retrieve it for the client. SQL Server is used by large companies as well as small businesses. There are several versions of SQL Servers available in the market, aimed at different target audiences. If you’re looking for a job as a system administrator or a database admin, or something along those lines, it’ll pay to be familiar with SQL Server setup. Take a quick introduction to SQL Server essentials with this course.

SQL Server Cluster

One of the major advantages of Microsoft’s SQL Server is the server clustering technology it supports. So what is a SQL server cluster exactly? When two or more servers share storage and access to that storage, they form a part of a cluster. They work as a single system and share the data. However, each server that is a part of the cluster can operate independently of the other servers. Each has its own operating system, RAM and disk space. Learn more about Microsoft SQL Servers with this course.

A server that is a part of a cluster is referred to as a node. The servers in the cluster communicate with each other all the time. If one of the nodes fails, the other nodes in the cluster will take over the resources of the failed node. The node will also handle the tasks of the failed node. The Cluster Service oversees this whole process, which is referred to as a “failover”. The Cluster Service will route traffic to the node that has taken over the responsibilities of the old node.

A SQL server cluster is basically a failsafe that keeps your operation up and running in the event that one or more servers fail. In large companies, it’s essential that the database they use should be accessible at all times, which is why they invest a lot of money in purchasing and maintaining multiple servers. Server failure can happen automatically, but sometimes it’s done manually too, in the event that the server needs to be updated or patched.

What Do You Need to Set Up a SQL Server Cluster?

SQL Server has an integrated failover installer. However, some groundwork needs to be done before you can use the installer. Setting up a server cluster can be expensive and complicated. It requires careful planning and budgeting.

The machines that form the nodes of the cluster need have to be powerful. Most of them are specially made and can support large databases. Some of the technology found in them is common: RAID 5 or RAID 10 arrays, more than 1GB ram for each node, special processor (Intel Xeon), stable hard drives (SAS or SATA) and network cards that enable them to communicate with the other nodes. The machines that are part of the cluster need to be compatible with each other as well.

To learn more about server and network architecture, you can take a look at this SQL Server course. If you’re looking for info on setting up a SQL Server Failover Cluster, check out the official guide here.

SQL Cluster Techniques

Server clusters that use SQL Server don’t increase the performance of your database (by sharing the work) and they don’t increase the available power (pooled power). Their sole purpose is to prevent the downtime caused by hardware failure.

Disk data can be made available to one or more servers in three ways:

  • Shared Disk

Shared disk nodes are configured with a Distributed Lock Manager. What was once an expensive setup (switches and extensive cabling was employed) has become less expensive lately. This is the least flexible technique- all nodes share access to the same disk. In the event the disk itself fails, the nodes would be rendered useless.

  • Mirrored Disk

The mirrored disk technique makes it less likely that you will lose data. Each node in the cluster has its own disk. Specialized software copies the content on each disk and transfers it to the other disks. This means that all the nodes are essentially using a disk that has the same data on it at all times. If one disk fails, the data would be preserved on the other disks. While this technique is more flexible than the shared disk technique, you need more resources to implement it. It may not be as efficient either, as system resources are always engaged in mirroring the data.

  • Shared Nothing

This technique is like the shared disk technique, save that each node on the server has its own disk to store data. In the event a server fails, the ownership of the disk that was being used by the failed node is transferred to another node in the cluster. The new node now takes over the disk and tasks of the old node. This model requires more resources than the shared disk technique, but provides more data security. However, it does not provide as much data security as the mirrored disk technique.

As you can see, setting up a SQL server cluster can be complicated. You have to choose the technique that best matches your needs. Maintaining a server cluster is also a long-term commitment, and specialists are often employed for the job. To learn more about maintaining and SQL Server, take this course. If you’re interested in learning more about SQL servers and database creation, this course can help you.  This is an emerging domain, so like we said earlier, learning about SQL Servers will definitely pay off.