Mainframe Business Continuance Via Asynchronous Replication: Mixing Synchronous and Asynchronous Replication for Maximum Cost-Effectiveness

by Nick Tabellion
August 1, 2004

Mainframe managers today are struggling to craft a cost-effective strategy for business continuance, of which traditional disaster recovery is only one part. The broader mandate of business continuance, however, makes it a more complicated and potentially more expensive task than mainframe disaster recovery. This is forcing managers to explore a growing set of options, especially asynchronous replication, and to assemble the optimum mix of technologies to achieve the organization’s business continuance and disaster recovery goals in the most cost-effective way.

The traditional mainframe disaster recovery strategy— synchronous mirroring—isn’t appropriate for all organizations or for the broader needs of business continuance. Business continuance refers to the ability to maintain business operations, even at a somewhat reduced level of service, in the face of any of a variety of problems that may impact the primary business center. It extends beyond IT to all operating units of the organization, its people and processes, although systems and data clearly play a central role.

Resuming business operations will likely entail recovering secondary applications and data as well as the organization’s primary applications and databases. It may involve positioning copies of data at multiple sites quite distant from the primary location.

Disaster recovery entails the ability to restore the organization’s primary production applications and data if a natural or man-made disaster temporarily or permanently makes those resources unavailable. In the mainframe environment, this traditionally has meant synchronous mirroring of data and applications across the corporate campus or metropolitan area.

 

Business Continuance Challenges

Events of the past few years have led most organizations to look beyond disaster recovery of the primary applications and address a broader set of business continuance needs, such as secondary applications and data. Given the more varied objectives, needs, and requirements of business continuance and the need to extend the range of conventional disaster recovery strategies, organizations are starting to look beyond synchronous mirroring and examine asynchronous replication and the opportunities it presents for addressing both business continuance and disaster recovery challenges.

 

Synchronous and Asynchronous Replication

In the z/OS environment, synchronous mirroring is the primary method of duplicating data for business continuance. With synchronous mirroring, data is written to the second (target) system at the same time it’s written to the primary system. The primary system doesn’t move to the next transaction or piece of data until the target system has acknowledged the previous transaction. So synchronous mirroring is the best way to ensure that the mirrored data is an exact real-time replica of the primary data. For this reason, it has become the standard mechanism for maintaining availability of critical production applications.