Microsoft Exchange server downtime can cost companies millions of pounds a year. Technical consultants therefore work with these organisations to reduce / minimise downtime through the implementation of high-availability systems and disaster-recovery systems. Building a geographically dispersed Exchange cluster is not a simple task; it requires proper planning, testing, deployment and validation. In this blog we aim to cover the basic steps during the planning stage for your company’s high availability/ disaster recovery plans. You have taken the first and most critical step toward deploying the system – recognising the need!
The process begins with the initial decision to implement an Exchange disaster-recovery system and continues as long as that system is in production. In the planning phase, you must answer these critical questions:
· What is the recovery time objective for the system?
· Based on the rate of change and expected growth, what bandwidth is required between the primary site and the disaster recovery site?
· What pieces of the system besides the Exchange server and processes them-selves must be monitored and recovered? Is there a minimum set of functionality that's acceptable for some time following recovery? If so, what is that subset?
· Are there site-specific error conditions that should be optimised for in the monitoring phase?
· Will automatic fail-over be allowed, or should administrator notification be the first recovery action?
· Which e-mail clients must be protected during fail-over? What access methods do they use? And how will these be migrated to the disaster recovery site during recovery?
The choice of a disaster recovery site should be the first decision you make. For some organisations backing up to a remote office is the perfect solution while others may look to collocated hosting centres that provide full redundancy for power and network connectivity. You need to ensure which ever route is take there are techniques and procedures in place for building a test environment, staff used to build the DR/HA environment should also be heavily involved in testing solutions and they should be hands-on in the deployment and validation stages.
The testing phase is often difficult because properly emulating a production Exchange environment within a test lab requires simulating cross-site network connectivity, user load, the influence of adjunct programs such as backup jobs and other factors unique to the specific environment. The closer you can get to a mirrored production environment within the test lab, the fewer issues you will see arise during deployment.
In testing, you are looking to answer questions such as these:
· Does the failover software perform as expected on both detection and recovery?
· Does the data replication software perform as expected in terms of speed and data consistency?
· Is there any noticeable performance impact on end users from the presence of the monitoring or data replication software?
· Are the various clients able to seamlessly migrate to Exchange running on the disaster recovery server?
Delivery of the solution should be straight forward if you assembled a team of experts and successfully emulated the production environment during the testing phase. Make sure you schedule sufficient time for the initial data mirror across site and subsequent testing of failovers to the disaster recovery site and back to the production server. Each of those tests should validate that client redirection works as planned and that all services needed for a fully functional Exchange environment are recovered.
Following the initial deployment, it is recommended that failover tests be made after any change to the Exchange environment (such as installation of service packs, introduction of new services, etc.). Carrying out regular system checks will avoid the disaster recovery system not working correctly and resulting in being unable to bring Exchange into service because of an administrative change that was not accounted for.
Open Minds HAS Ltd has been working with customers to deploy Exchange Server High Availability for over 10 years. To speak to one of our experts please contact us on 0121 533 7178
