Google (s goog) for the past three years has been trying to upend the enterprise market’s leading software suite, Microsoft (s msft) Office, with its cloud-based Google Apps. With cloud services now being widely adopted in the enterprise, the Mountain View, Calif.-based company’s offering is starting to pull ahead.

Google currently claims some 2 million entities as Google Apps users, from small businesses to large corporations such as Motorola (s MOT) and Genentech (S dna) to cities such as Los Angeles and educational institutions such as Yale University. “Google Apps are growing quite rapidly, especially in the educational sector,” Rajen Sheth, Google Apps senior product manager, told me. The number of people actively using Google Apps now tops 20 million.

The primary driver of Google Apps is no doubt Google Mail. Based on the extremely popular and excellent Gmail service, Google Mail is gaining popularity because it works with established products such as Microsoft Outlook and the BlackBerry (s rimm) Enterprise Server. When I asked Sheth if Google was going to announce Google Buzz for the enterprise, he said: “We are planning to roll it out for businesses but with requisite policy and privacy controls.” Though when that’s likely to happen he wouldn’t say.

Google has seen a marked change in people’s attitudes towards cloud-based services such as Google Apps, which has resulted in it signing on dozens of large companies as customers in the last year alone. “Three years ago people said no way, and now more and more organizations see the benefits of cloud-based services,” said Ben Lutch, director of engineering for Google Apps. As he and Sheth explained, Google Apps’ biggest advantages are its availability and its disaster recovery features, the result of its ability to do “synchronous replication” very quickly and very cheaply.

All Google Apps are written on top of the Google File System, which gives the company the unique ability to not only write data to multiple locations insider a specific data center, but also across the multiple data center locations that make up the global Google infrastructure. Since these globally dispersed locations are connected to each other with very high-speed fiber connections, Google can literally save bits of your information across the globe. (Related: Google’s Infrastructure Is Its Strategic Advantage.)

“Because we are using a vertically integrated set of hardware and software, that essentially frees us from being dependent on third parties, where as other companies are dependent on these third parties,” Lutch said. “We do this to ensure that we are front and center of our infrastructure needs and we don’t have to wait for others to really help us.” Google has developed its own hardware — both computing- and communications-oriented — to work with its own software, which is essentially the Google File System.

“Software is our secret sauce,” boasted Lutch. “Our infrastructure is built on the assumption that there is and will be a failure somewhere so we have put an emphasis on working around those failures. We have done so by focusing primarily on software.”

A post on the Google Enterprise Blog offers additional detail:

In larger businesses, companies will add a storage area network (SAN), which is a consolidated place for all storage. SANs are expensive, and even then, you’re out of luck if your data center goes down. So the largest enterprises will build an entirely new data center somewhere else…..But if, heaven forbid, disaster strikes both your data centers, you’re toast.

How do you know if your disaster recovery solution is as strong as you need it to be? It’s usually measured in two ways: RPO (Recovery Point Objective) and RTO (Recovery Time Objective). RPO is how much data you’re willing to lose when things go wrong, and RTO is how long you’re willing to go without service after a disaster.

Enterprises without SANs may be literally trucking tapes back and forth between data centers, so as you can imagine their RPOs and RTOs can stretch into days. As for small businesses, often they just have to start over….For Google Apps customers, our RPO design target is zero, and our RTO design target is instant failover.

To backup 25GB of data with synchronous replication a business may easily pay from $150 to $500+ in storage and maintenance costs- and that’s per employee. That doesn’t even include the cost of the applications. The exact price depends on a number of factors such as the number of times the data is replicated and the choice of service provider. We also replicate all the data multiple times, and the 25GB per employee for Gmail is backed up for free.

Related GigaOM Pro Research:
(subscription required, free trial available)

• Report: Social Media in the Enterprise
• Report: The Real-Time Enterprise
• Threats Loom Large for Microsoft’s Email and Collaboration Platforms
• Google Buzz’s True Home Is in the Enterprise

Feature image courtesy of Flickr user OmarCaf, in-post image courtesy of Flickr user Andy Ciordia