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Active/Active Sites Helps Distribute Workloads During Outages


As enterprises have become more dependent on IT, their continuous availability, disaster recovery (DR) and business continuity requirements have become more demanding. Government regulations are more stringent as well.

In fact, the Federal Reserve Board, Office of the Comptroller of the Currency and the Securities and Exchange Commission specify in their report, “The Interagency Paper on Sound Practices to Strengthen the Resilience of the U.S. Financial System,” that recovery from a disruption must happen quickly. “The core clearing and settlement organizations should develop the capacity to recover and resume clearing and settlement activities within the business day on which the disruption occurs with the overall goal of achieving recovery and resumption within two hours after an event,” the report says 1.usa.gov/1krgPek.

IT outages cost more, too. Research firm Aberdeen Group found that between June 2010 and February 2012, the average cost per hour of downtime increased by 65 percent (http://bit.ly/1kw4sio). Internet-based customer interaction and social media make IT service interruptions widely known very quickly.

A Paradigm Shift

To address today’s stringent requirements, IBM created the Active/Active (A/A) Sites solution. A/A Sites is two or more sites separated by extended distances running the same applications and using the same data to provide cross-site workload balancing, continuous availability and DR. It’s a fundamental paradigm shift from a failover model to a continuous availability model.

A/A Sites is designed to largely eliminate planned outages (e.g., application, database management system, software and site maintenance) while mitigating the impact of unplanned outages (e.g., application and site failures). There are redundant workload instances for each workload. Each workload instance is executing on a separate sysplex, and the sysplexes reside in different regions separated by extended distances. When planned or unplanned outages occur, A/A Sites switches to an alternate workload instance.

The GDPS*/Active-Active (GDPS/A-A) product was developed to implement the A/A Sites solution. GDPS/A-A control software manages and monitors the A/A Sites configuration. GDPS/A-A can start and stop sysplexes, workloads and replication; perform planned and unplanned workload and region switches; and manage disk replication. Additionally, it has extensive monitoring. When it detects a condition affecting the capability to perform workload or region switches, it generates an alert about the outstanding issue.

The GDPS/A-A Sites Concept consists of sysplexes deployed in two or more regions, with the same workloads and data objects (see Figure 1). Network connections are routed to workload instances on each sysplex by workload distributors (routers). Most routers support the needed Server/Application State Protocol (SASP) protocol. GDPS/A-A uses SASP to provide guidance to the routers to route connections, thereby adding the capability to switch between workload instances.

DB2*, IMS* and VSAM data is synchronized between sysplexes using software-based asynchronous replication, which consists of capture engines and apply engines. Capture engines monitor the source database management system (DBMS) for committed transactions, which are replicated from the source DBMS to the target DBMS, and the apply engine applies them at the target DBMS. Typically less than one second latency occurs between a source and target DBMS. This allows the sysplexes to be separated by extended distances.

David Petersen is an IBM distinguished engineer for the System z platform.



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Active/Active Sites Helps Distribute Workloads During Outages

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