Setting up and managing a continuous replication environment

The goal of continuous replication is to try and maintain identical copies of an application's VSAM spheres between two sites.

You can do this by operating Data Replication for VSAM all of the time, replicating changes that are made at a source site and applying them at a target site.

Data Replication for VSAM uses asynchronous data capture, so while the source VSAM clusters are changing, individual records are not point-in-time consistent. However, the goal is to configure the system so that a change that is made at the source site is applied to the target within a few seconds under normal operating conditions.

To support this model, the source and target VSAM clusters should be structurally identical so that any changes that a source application makes can be applied to a matching target VSAM cluster. This environment also requires the source and target VSAM clusters to contain the identical contents. To prevent apply failures, an individual record should only be updated at the source site. You can configure systems with key partitioning such that different keys are updated on different sites; in that configuration each key is updated in one direction to avoid apply failures. Further, you can use latency information to determine when it is safe to change the direction of which site particular keys are initially applied at and which site they are replicated to. For example, if a particular key has not been updated in the past hour and latency is sub-second, then a new change for that key can be directed to either site as its source site.

You can use the conflict exit to compensate for source and target discrepancies when the contents of the source and target VSAM clusters are not the same.