Originating Author: Nicholas Allen
Anyone contemplating remote replication must understand that the planning phase is the most important step. Getting it right from the start can save major hassles down the road. Disk array-based remote copy infrastructures have been available and in use for more than a decade. When properly configured and deployed, they are capable of providing a timely recovery from a variety of failures, including the loss of an entire data center site.
And the place to start is establishing your RPO and RTO (recovery time objective and recovery point objective) Depending on the RPO one then chooses synchronous or asynchronous replication. The choice of replication technology will have performance impacts that customers must understand. Specifically, the amount of data pushed through the link, the link bandwidth, and associated latencies can dramatically and detrimentally effect performance in a synchronous environment. Asynchronous replication will maintain performance as latencies increase but will have the drawback of creating greater exposure to data loss as write data queues up in the write history log. An aggressive RPO dictates synchronous replication and therefore a low latency network link – typically a link that is 100 miles or less.
Once that choice is made, the next planning phase is research. Read all the manuals, white papers, and case studies you can find – both from the vendors as well as independent research such as Wikibon. Of course, one should speak with as many users as possible who have a similar implementation. Asking industry analysts’ opinion is also wise.
After that it becomes mostly a sizing and testing exercise. Since HP’s EVA falls in the mid-range category, will it have enough power for the full life of this application? Will it scale with growth? What happens if one of the EVA’s two controllers fails or is shut down for an upgrade? Can this planning and implementation be leveraged into a high-end array, or is it back to square one?
Next comes testing. Test, test, and test some more. Then test it again. If possible get HP to test your application at one of its centers or install test systems at your sites. Be sure to pursue extensive fault injection. Test not only fail-over, but also fail-back to the original site. Do this several times.
Action Item: when it comes to array-based replication, up front planning is first and foremost. This should be followed by extreme testing. Users should free up and allocate extensive resources for such a project.
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