october 3

Choosing the right data-replication option
What are the key factors to consider in addressing a data-replication requirement?
Computerworld Opinion by Jim Damoulakis

http://www.computerworld.com/action/article.do?command=
viewArticleBasic&taxonomyName=storage&articleId=9003824&taxonomyId=19&intsrc=kc_feat

A while ago, I wrote about the growing number of disaster recovery options available to companies (see "Small companies need DR too"). The selection of replication, snapshot and continuous data protection technologies continues to grow. While it's great to have choices, it also creates a problem -- how do you choose the right option?

In the storage world, we often take somewhat parochial view and assume that the term replication implies array-based replication. In reality, replication can happen at the application, database, file system, operating system or network levels as well, and the truth is that a "one size fits all" replication may no longer make sense. There are trade-offs to each approach, and depending on the decision criteria, each one can be a valid solution.

So what are the key factors to consider in addressing a data replication requirement? Here is a list of questions that can help to steer you to the right technology:

• What are the recovery time objectives and recovery point objectives? In other words, how critical is the data to the business?

• What are the performance characteristics of the application? Is the application transaction-oriented with a high data I/O rate, or are data changes less frequent?

• How far away is the replication site? The distance required may preclude some choices, such as synchronous replication.

• How complex is the application? Is it distributed across multiple servers? If so, some forms of replication may be better suited to ensuring data consistency across the entire application than others.

• What are the scalability requirements for the replication system? Is this a point solution for a small number of applications, or does it need to scale to support hundreds of servers?

The answers to these questions will help whittle down the list of appropriate technologies to a few, and more importantly serve to focus and prioritizes needs. Then the decision process can turn to that all-important final consideration -- cost!

Jim Damoulakis is chief technology officer of GlassHouse Technologies Inc., a leading provider of independent storage services. He can be reached at jimd@glasshouse.com.