If an on-premises server fails, IT departments cut over to a backup system immediately. But what do you do when your cloud computing service goes on the blink?

As more companies plug into the cloud, IT professionals are trying to answer that question. And fast. Last week, Google's Gmail went down for two hours, the second time in two weeks. Citrix's GoToMeeting and GoToWebinar were temporarily unavailable. A month ago, Amazon.com's Simple Storage Service was out of commission for an excruciating eight hours.

"Outages are just a reality," says Tim O'Brien, director of platform strategy for Microsoft. "Microsoft is a reputable company, Google's a reputable company, and Amazon's a reputable company. Even if you do your due diligence, you still have to manage around these risks, even if the risks are particularly low."

All of which is forcing customers to rethink their dependency on software as a service and other cloud services, and devise strategies for the inevitable breakdowns, as market researcher Harris Interactive has done. "We have some users who absolutely live and die by that database and the data in Salesforce.com," says Dan Chiazza, Harris Interactive director of global sales operations. "For them, they would have no business coming into work if it wasn't up."

There are steps companies can take to minimize the risk, including storing data with multiple service providers and regularly backing up SaaS data on on-premises servers. Forrester Research analyst Liz Herbert recommends that customers ask whether a prospective service provider has geographically dispersed redundancy built into its architecture and how long it would take to get service running on backup. Salesforce provides visibility into its system reliability at trust.salesforce.com.

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Be wary of service providers with a short track record. The cloud computing market is full of startups, and while new service providers shouldn't be shunned, extra diligence is in order. Ask about their data center facilities, customer references, and any assurances they can provide that your data and applications will stay online. Archiving-as-a-service startup Casdex has gone so far as to set aside funds to ensure that its service keeps running for six months even if Casdex itself runs into financial trouble, says CTO David Barley. The Linkup, a storage service for consumers, closed down Aug. 8, leaving some customers with no way to access their data.

When negotiating for cloud computing services, IT departments should insist on service-level agreements that have some teeth to them, Herbert says. SLAs that guarantee a high level of uptime aren't necessarily standard. Salesforce doesn't commit to uptime thresholds -- unless you insist on it during negotiations, she says.

Most SLAs reimburse customers for lost service, but not for revenue lost as a consequence of service outages. Amazon applies a 10% credit if S3 availability dips below 99.9% in a month, and last month's outage forced Amazon to make good on that policy. "That's all well and good, but doesn't make the business whole relative to the damage," says Gartner analyst Rob DeSisto.

STOPGAP MEASURES
Another coping technique: Google, Salesforce, and some other SaaS providers offer PC applications that tie into their services, so users can work offline. Microsoft will do the same with the multitenant versions of its Exchange Online, SharePoint Online, and Office Communications Online services, which are in beta testing. Microsoft's Dynamics CRM Online is already available as a multitenant offering.

In the case of Google and Salesforce, their PC applets are intended for on-the-go and disconnected users, but they can be stopgap measures during a service outage, too. Harris Interactive recommends that its users download Salesforce's offline edition, which contains a copy of contacts and accounts and lets users synchronize their data when they regain online access to Salesforce. The drawback is that the offline versions of SaaS applications generally aren't as feature-rich as the cloud ones.

Another tactic is to limit your dependency on cloud services for business-critical processes. "You need to be thoughtful about how use you use cloud resources, so that the things you do have lower risk. If it takes an extra day to run, you don't really care," says Russ Daniels, VP and CTO of Hewlett-Packard's cloud services business. "Be thoughtful about where this stuff sits, rather than imagining that your existing systems will be replaced by stuff in the cloud and it will all be OK."

Clouds Vaporize Aug. 12 Scheduled maintenance for Apple's MobileMe service has a ripple effect on users Aug. 11 Glitch in Google Gmail's contacts system causes a two-hour outage for some users Aug. 7 Citrix blames GoToMeeting and GoToWebinar service disruption on a surge in demand Aug. 6 Google Gmail out of commission for up to 14 hours for some users July 20 Internal system problem causes Amazon S3 service to be inaccessible for up to eight hours

There's also a choice to be made between multitenant services, in which multiple SaaS customers are hosted on the same system, and single-tenant services that devote one or more servers to a customer. Microsoft will offer both multitenant and single-tenant versions of its Online applications. The single-tenant version will cost a bit more, but it also will give customers peace of mind knowing that their applications are insulated from others'.

The worst-case scenario would be your SaaS provider going out of business, as The Linkup did recently. Storage company Iron Mountain has developed a safety net for companies worried about that risk. Its SaaSProtect Escrow service lets IT departments store data or applications with Iron Mountain and access them if the SaaS provider goes belly up. "We can sit in the background and help create at least some safety," says Iron Mountain CTO Fred Engel.

Some companies will seek to get the benefits of cloud services--the ability to quickly provision applications as needed, for example--without the disruptions by building "private clouds" in their own data centers. Others will wait until cloud service providers get more experience and see that change reflected in fewer and shorter outages and SLAs that demonstrate greater confidence in service availability. The early adopters of cloud services, meanwhile, need to develop fortitude--and backup plans.