There is a large degree of overlap between High Availability and Disaster Recovery. The terms are often used together or in place of each other, and the terms Business Continuity and Fault Tolerance may also arise.
At Cheddon Limited we see an important distinction between these terms.
Fault Tolerance, High Availability, and Resilience focus on maintaining up-time, whereas with Disaster Recovery and Business Continuity the focus is on recovery time.
The relationship between Business Continuity and Disaster Recovery is simple in itself, Disaster Recovery is a subset of Business Continuity.
Business Continuity or Disaster Recovery do not need to make any provision for High Availability or Fault Tolerance. A Small Business Disater Recovery Plan may be as simple as a backup tape and a credit card.
In a non-clustered Microsoft Exchange server environment, through application of documented and tested disaster recovery procedures it is possible to restore messaging dial tone in 90 minutes or less.
At a minimum you should plan for Disaster Recovery. Along the way, High Availability and Fault Tolerant hardware and applications may reduce the potential impact of disaster situations that can arise.
The key to a successfully disaster recovery is the plan itself.
“A plan of action to recover from an unlikely event of a severe or catastrophic business disruption.”
You may have the most advanced infrastructure and employ the most highly trained people, but in the event of a disaster everything will depend on the quality of any documented procedures that you have in place, and the level of familiarity your staff have with them.
What is important is that everybody involved in the declaration of and recovery from a disaster is familiar with the processes and procedures to make it happen.
More than at any other time, during a recovery situation people, process and technology take equal importance in the smooth running of a business.
A tried and tested disaster recovery plan for Microsoft Exchange Server should address the following scenarios at a minimum:
Recovery Databases. Using native recovery database technology it is possible to restore an individual mailbox or even an entire mailbox store with no adverse or noticeable effect on existing service provision.
Messaging Dial Tone. Messaging dial tone allows you to restore a “basic” e-mail service, where your organisation can send and receive e-mail and has full access to an e-mail service, but does not have immediate access to legacy data.
Full System Recovery. Service has been restored to the state it was in before the disaster occurred.
Remember that “Risk can be defined as Probability times Cost.”
Unlikely as you may think it is that you could ever have a service failure, quantify the cost involved in lost productivity and recovery. Then decide if it’s a risk you can afford.
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