“Today's enterprises don’t have the luxury of failing and then recovering from that failure when going offline isn’t an option – and so the 'dark DR' model fails them,” he adds.
Foster disagrees with that statement. “If you are still operating backup and recovery and DR like it is 2005, then yes that statement may be correct, but the reality is that customers are modernizing how they execute on DR and backup as their infrastructures and architectures have matured and changed. When they don’t do this, outages can occur due to the no integrate fashion in which protection and DR decisions are made.”
In addition, the primary server’s normal workflow must be redirected to the secondary server, which becomes, at least temporarily, the new primary server. This redirection can require significant amounts of manual configuration, with two IT teams (one at each location) working overtime to enable and troubleshoot the switch. Similar reconfiguration applies to DNS, networking, replication topology, and other infrastructure elements. Testing requirements are massive, and additional IT staff must step into place at the secondary facility while the original IT team remains pinned down trying to get the primary facility back online.
“Of course, as we’re watching the big trends around 'software is eating the world' and 'every company is becoming a software company,' there are fewer and fewer organizations for whom downtime is acceptable. DR often means at least several minutes, if not more, of downtime, and of course, because you’re bringing an idle system online all of a sudden, it may not start operations smoothly. But yes – active/active architectures are best suited for organizations that cannot tolerate downtime,” Barney said.
Joseph George, vice president of product management at Sungard AS, said he wouldn’t frame the debate between the two architectures purely in terms of efficiency, because often the biggest deciding factor for what resiliency tier a business selects is based on what companies can afford. “Clearly, if cost was not a factor, every business would have [high-availability] systems. But they typically can only afford (and need) that level for the most mission critical systems and applications,” he said.
“It is important for enterprises to 'tier' their applications to help manage the economic balance between risk and the investment to mitigate. Tiering applications, as well as mapping their interdependencies, enables optimal recovery order sequencing and allows for the most cost effective availability program for the level of application downtime and data loss the organization can afford based on business impact,” he added.
Warm DR is fine
Swike said the majority of enterprises don’t really need active/active DR. Warm DR meets their needs. With appropriate bandwidth between sites, an RPO of seconds and technical RTO of minutes-to-hours is very achievable. “The technology is only part of the story though: there has to be discipline and time given to the process of DR. Having servers replicated is a great step, but if you don’t test it regularly how would you know it’s even going to work?”
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