Real-Time Remote Data Mirroring

Primitivo Cervantes

When planning for a disaster, there are many issues to consider and resolve. Some of these issues are resolved with the use of a remote location as an emergency production site in case the primary site is unavailable due to a disaster. In this situation, a remote data center is set up with systems similar to the primary production systems. This remote disaster recovery site is usually connected to the primary site via a network.

Even with a remote disaster recovery site, there are still many issues to consider. The remote site is usually not in use during normal production hours and is a cost center until it is used as a recovery center. You must determine, for example, whether you want the exact system as the primary site or whether you can do with reduced performance during an emergency. You must decide whether you can afford to lose some data in an emergency or whether you need all of the most current data when bringing the systems online at the remote site. You must also consider how current the data must be and how much you are willing to pay for it. In this article, I will discuss various data-replication techniques and their associated advantages and disadvantages. I will also describe costs associated with these techniques and describe cases where it might be justifiable for them to be implemented. I will also describe an installation of one of these techniques, using IBM's HAGEO product to replicate data in real-time to a remote site.

Before I get into the data-mirroring techniques, I will explain the types of data that clients usually mirror. There are three basic types of data that are usually required to run a customer application: operating system data, database data, and non-database application data. Operating system data consists of the programs and files needed to run the operating system such as IBM's AIX.