How much availability, or up-time, is “good enough" for absolutely critical building automation and security systems.

Security System Availability: Understanding Your Options

As building automation and security systems become increasingly reliant on server technology, ensuring the availability—or uptime—of the applications running on those servers is absolutely critical. But how much availability is “good enough”? And what’s the best way to achieve that level of availability?

To answer those questions, it’s important to understand the three basic approaches to server availability:

1. Data backups and restores:

Having basic backup, data-replication, and failover procedures in place is perhaps the most basic approach to server availability. This will help speed the restoration of an application and help preserve its data following a server failure. However, if backups are only occurring daily, significant amounts of data may be lost. At best, this approach delivers approximately 99 percent availability.

That sounds pretty good, but consider that it equates to an average of 87.5 hours of downtime per year—or more than 90 minutes of unplanned downtime per week. That might be good enough for a business application that is not mission critical, but it clearly falls short of the uptime requirements for building security and life-safety applications.

2. High availability (HA)

HA includes both hardware-based and software-based approaches to reducing downtime. HA clusters are systems combining two or more servers running with an identical configuration, using software to keep application data synchronized on all servers. When one fails, another server in the cluster takes over, ideally with little or no disruption. However, HA clusters can be complex to deploy and manage. And you will need to license software on all cluster servers, increasing costs.

HA software, on the other hand, is designed to detect evolving problems proactively and prevent downtime. It uses predictive analytics to automatically identify, report and handle faults before they cause an outage. The continuous monitoring that this software offers is an advantage over the cluster approach, which only responds after a failure has occurred. Moreover, as a software-based solution, it runs on low-cost commodity hardware.

HA generally provides from 99.95 percent to 99.99 percent (or “four nines”) uptime. On average, that means from 52 minutes to 4.5 hours of downtime per year—significantly better than basic backup strategies.

3. Fault-tolerance (FT)

Also called an “always-on” solution, FT’s goal is to reduce downtime to its lowest practical level. Again, this may be achieved either through sophisticated software or through specialized servers.

With a software approach, each application lives on two virtual machines with all data mirrored in real time. If one machine fails, the applications continue to run on the other machine with no interruption or data loss. If a single component fails, a healthy component from the second system takes over automatically.

FT software can also facilitate disaster recovery with multi-site capabilities. If, for example, one server is destroyed by fire or sprinklers, the machine at the other location will take over seamlessly. This software-based approach prevents data loss, is simple to configure and manage, requires no special IT skills, and delivers upwards of 99.999 percent availability (about one minute of downtime a year)—all on standard hardware.

FT server systems rely on specialized servers purpose-built to prevent failures from happening and integrate hardware, software and services for simplified management. They feature both redundant components and error-detection software running in a virtualized environment. This approach also delivers “five nines” availability, though the specialized hardware required does push up the capital cost.

Making server availability a cornerstone of your building security automation strategy pays dividends both in terms of day-to-day management and when situations arise that test your security. With the right strategy up front, your building’s security systems will be there when it really counts today and in the future. In today’s constantly changing, “always-on” world, that’s all the time.

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Robert Otto is Director of Product Management at Stratus Technologies. He is responsible for Stratus’ software product lines, designed to prevent downtime and ensure uninterrupted operation in an always-on world. Robert has been responsible for the successful market delivery of hardware and software products across a wide range of industries for 20 years and has served as an advisor to several successful start-ups.

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