Preparing Disaster Scenarios

DBAs are custodians of the data owned by internal company departments such as marketing and finance, so they must inform the data owners of potential problems that might occur during replication. You should effectively communicate the following information to your business partners:

  • The maximum data loss that can take place in a given replication setup
  • The length of time the system would be down in the worst-case scenario
  • The expected phase lag between the time a transaction replicates from the Publisher to the Subscriber and from the Subscriber to the Publisher.

You can give the data owners accurate estimates only when you clearly understand what happens during replication and know how to restore your system when something goes wrong. A helpful communication device is a disaster-scenario chart in which you list the possible disaster scenarios that can occur in a replication setup. For each scenario in the chart, you provide the maximum data loss and the corresponding restore strategy to ensure data consistency across Publisher and Subscriber. Here are a few disaster scenarios you can list:

  • Publisher database goes down and log isn't available
  • Publisher database goes down and log is available
  • Distributor database goes down and log isn't available
  • Distributor database goes down and log is available
  • Connection between Publisher and Distributor is down

Demonstrating that you had the foresight to consider several possible disaster scenarios and integrate them into the design of your replication project will inspire the confidence of the data owners. Your due diligence will show them that you've made every effort to minimize the damage and the cost of data restoration in the event of a disaster.

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