What should be the distance between your Primary Site and DR site?
Article by Karan Kirpalani
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A lingering question in the minds of most CIOs while planning a DR site (secondary site) is what should be the ideal distance between their primary and secondary sites. A question that deserves due diligence and consideration, no doubt. My answer to this question is that, ‘It depends’. There is no hard and fast rule governing the distance between your primary and secondary data centers except the fact that both these sites should be far enough from each other. The reason – when some unforeseen disaster strikes the primary site, the secondary site should be able to plug in and start running so that there is no business disruption.
Both the sites cannot be located close to each other simply because of the fact that a natural calamity or a man-made disaster should not be able to affect both the sites. But how far is far enough…. give me a number I can consider.
The chart below gives a fairly good idea about companies planning their DR sites in 2007 and 2010. An interesting observation here is that between 2007 and 2010, survey respondents reported shorter distances between primary and secondary data centers. In 2007, 22% of respondents reported that the distance between their primary data center and farthest backup data center was greater than 1,000 miles, while in 2010, only 12% claimed this distance. In 2013, 13% claimed that the distance between their primary data center and farthest backup data center was greater than 1,000 miles. A number similar to the previous year.
So what do all these results show?Is far away really better? Not necessarily, consider the following facts:
Distance may not mean safety
Just for the reason that your primary and DR sites are farfrom each other does not mean that these sites are not prone to similar risks. For example, an organization that has their primary site in Mumbai and a recovery site in Chennai– though the sites are separated by a considerable distance, they can still be impacted by similar natural forces – cyclonic storms, heavy rains, flooding etc.
Too far can be too risky sometimes
Sites that are located far apart can face problems related to latency and bandwidth. Thus, replicating data between these two sites can become expensive and time consuming. In such a case Recovery Point Objectives (RPO) may get impacted.
A recent report from Gartner (How to Identify the Best Data Center Locations for Disaster Recovery, January 10, 2014) noted that if achieving a stringent RTO requires remote data mirroring, then the two sites should be within 60 miles of each other because of network latency concerns. “At more than [60 miles], even with tuning capabilities, latency issues will begin to impact performance and make synchronous or active/active recovery model unrealistic,” the report cautioned.
The People Equation
If your Disaster Recovery (DR) planning is such that it requires your staff to physically access a data center that is situated at a distance from the main office, the distance itself can become a barrier to recovery. Should a disaster strike, your employees may be unable or unwilling to travel long distances to the secondary site, either due to personal reasons or difficulty in getting transportation.
In such cases, cross training staff is essential; ideally you should plan for two to three teams that are prepared to deal with recovering critical business operations simply for the fact that you may not know who would be available in the event of a disaster.
So here we are again – how far is far enough? Before answering that question consider the following:
- Whether your client based is spread locally, regionally or nationally and the criticality of the services during a local or a regional event.
- Whether the alternate location has adequate risk mitigation practices to safeguard against the effects of a regional outage – redundant power supply and telecommunication facilities, storage, ideally with redundant network connectivity and access between sites and how long can the company continue to operate as such.