Is your business playing Russian Roulette with system availability?

Server clustering and data mirroring for high availability

Every year, I hear dozens of horror stories from customers about server and network outages and the resulting loss of data and productivity. For a brief moment, some network users may find an outage a bit charming, as older colleagues lean back and reflect, "This is the way it was back in the '70s – no Internet, no e-mail, not even a fax machine. Just typewriters, phones, and Uncle Sam's mail."

Such nostalgia is invariably short-lived, though. Today, it's all about immediacy of access to information, applications and one another. Even small enterprises are increasingly online, mobile and Web 2.0-driven, to the point where IT is no longer just a business tool. It is business – the heart and the circulatory system through which most transactions flow. If your IT systems fail, your daily operations follow – and if the outage lasts too long, your business may fail.

So small-to-midsize businesses should ask themselves how they can create a high-availability infrastructure that responds robustly to new-age business challenges and disruptions. Server clustering and data mirroring can play an important role in implementing high availability. They can also serve as a cornerstone to an effective business continuity and disaster-recovery strategy, and – good news – they can be very affordable.

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Every year, I hear dozens of horror stories from customers about server and network outages and the resulting loss of data and productivity. For a brief moment, some network users may find an outage a bit charming, as older colleagues lean back and reflect, "This is the way it was back in the '70s – no Internet, no e-mail, not even a fax machine. Just typewriters, phones, and Uncle Sam's mail."

Such nostalgia is invariably short-lived, though. Today, it's all about immediacy of access to information, applications and one another. Even small enterprises are increasingly online, mobile and Web 2.0-driven, to the point where IT is no longer just a business tool. It is business – the heart and the circulatory system through which most transactions flow. If your IT systems fail, your daily operations follow – and if the outage lasts too long, your business may fail.

So small-to-midsize businesses should ask themselves how they can create a high-availability infrastructure that responds robustly to new-age business challenges and disruptions. Server clustering and data mirroring can play an important role in implementing high availability. They can also serve as a cornerstone to an effective business continuity and disaster-recovery strategy, and – good news – they can be very affordable.

Clustering and mirroring for high availability

Server clustering is the answer for several objectives: creating scalability, load balancing and, of course, increasing system availability. Clustering for high availability allows the automated failover between servers in the cluster, providing close monitoring of applications and all their components, including operating system, server hardware, networking and storage.

The clustering software determines when to perform a failover by continually checking each application's "heartbeat" signal, and if one system has a problem, the application on another server in the cluster takes over. To the outside world, the cluster appears to be a single system, but intelligent redundancy within it creates high availability.

Application availability is only half of the IT requirement. The data that applications create and use must be equally available in order for business to continue. Disk mirroring is the recording of redundant data on two partitions of the same disk or two separate disks, for fault-tolerant operation.

Mirroring is a central component in the highest level of data protection and disaster recovery, and it differs from ordinary backups, which simply replicate a complete volume at specific points in time, often for use in testing. Mirroring creates dynamic, real time copies of data volumes, which further reduces the amount of data at risk of loss. Mirroring can be done using Level 1 Redundant Array of Independent Disks (RAID) features. RAID can be provided through the motherboard or a controller card, or built into a dedicated disk array.

Benefits and challenges

Server clustering provides three key benefits:
 High availability: Designed to avoid a single point of failure.
 Scalability: Computing power can be increased by adding more processors or computers.
 Manageability: Appears as a single-system image with a single point of control.