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How to modernize Systems Network Architecture applications

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Companies that have requirements for disaster recovery (DR) across multiple data centers have had challenges in providing support for Systems Network Architecture (SNA) applications. These applications manage transactions by synchronizing responses across multiple stakeholders of a transactional flow. Examples of SNA applications are automated teller machines, medical records reporting and background checks for financial or insurance purposes. SNA does have support for high availability designed into the protocol implementation. High-Performance Routing (HPR) is a protocol that supports nondisruptive data connections between SNA nodes such that applications are not affected by a network outage.

Nondisruptive data connections for SNA are a valuable feature to have, but this does not meet the expanding requirements of DR across multiple data centers. The latest requirement for DR is to support what is known as Active-Active. This provides the ability to dynamically switch between back-end application providers on data centers so that if one data center becomes unavailable (planned or unplanned), the client applications using those back-end applications continue to run. Active-Active also supports data centers across longer distances than normal DR implementations.

Disaster recovery verses continuous availability

In the past, DR has been implemented using a dedicated backup site that was maintained in a “cold state.” Application data is mirrored or replicated to this backup site for real-time updates to a server farm. In the case of a disaster or outage on a primary site, applications can be started in the backup site from this cold state. The minimum time to recover from a disaster or a planned shutdown might take four to eight hours. This time to recover depended on the applications, the amount of data and the journaling of transaction records to synchronize recovery. Limitations on distances were also imposed due to the speed of light and the propagation of data being replicated to the backup site. A maximum of about 150 miles was the limit for doing real-time writes of data in mirroring application data.

With Active-Active implementations, as in the recently announced IBM Multi-site Workload Lifeline V2.5, applications can support Active-Active solutions based on TCP/IP workloads. Workload data can be replicated between sites at unlimited distances. The mean time to recover can be less than two minutes, not hours. Using TCP/IP intelligent load balance advisors from Multi-site Workload Lifeline, data centers do not have to be considered “backup” centers or be in a cold state; they can be active so that workload can be distributed among sites. This provides continuous availability across sites so that there is no downtime when a disaster or planned outage takes place.

Taking advantage of workload provisioning

My recent discussion on “How to migrate SNA applications to cloud” described how transactional SNA applications can be migrated to TCP/IP workloads connected to a domain of servers. This cloud implementation provides the needed support for Active-Active such that SNA applications can now take advantage of the workload intelligent load balancers. This means SNA applications on distributed platforms can access back-end applications in a continuously available manner.

The following diagrams show a before and after implementation. The first figure is a traditional SNA implementation where SNA applications have a direct connection to a mainframe where back-end applications reside. The whole data center must be duplicated, and only one data center can be active at a time. Thus, the secondary center must remain in a cold state, waiting for an event to require it to be started and act in place of the primary data center applications.

The second figure shows how a cloud implementation can use intelligent load balancing from Multi-site Workload Lifeline to manage access to either data center concurrently. This way, both data centers can be active, and continuous availability is realized.

SNA Cloud Continuous Availability
Figure 1: Before migration with significant overhead

SNA Cloud Contiuous Availability after migration
Figure 2: After migration with reduced overhead

Assuring availability is a benefit of migrating SNA applications to a cloud implementation. This migration will pay for itself by using continuous availability rather than disaster recovery.

If you would like to see other benefits of modernizing SNA applications, chime in with a comment below or contact me on Twitter @jefsmith5221.

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