In cases where cost and failover time are important issues, you must create failover scenarios for your critical data systems that won't break the bank and won't have long failover times. The answer is an HA solution, which offers the ability to fail over locally to readily available and preconfigured systems designed to stand in for the failed system.
HA systems offer several advantages. You can generally fail over very quickly, using "hot-standby" servers that don't require powering up, rebooting, or configuration. This also means that you don't have to reroute end users because the failover systems are usually on the same IP segment as the primaries.
However, when implementing an HA system, you must be aware of two major drawbacks. Fortunately, you can easily overcome both issues with the proper planning.
HA systems share the first drawback with local disaster recovery solutions. A loss of the physical site could result in the destruction of the backup systems as well as the production systems.
You can avoid this by either replicating data off-site (to much fewer servers and with much less infrastructure) and/or by removing tape backup media to off-site storage locations. Either of these steps can provide the ability to recover from both small and data-center-level disasters, albeit with different recovery point objectives.
The second drawback is that failover solutions of any kind—both local and remote—are much more complex than simple DR solutions. You must configure additional server systems to stand in for one or more production systems, keeping in mind that some systems will not support many-to-one failover.
While this drawback is not necessarily difficult to overcome, you can't overlook it. Make sure to prepare for the implementation with training, professional services, and other methods of getting over the learning curve.
HA systems allow organizations to fail over much faster than remote failover, and they offer a greater level of protection for critical systems than DR alone. If you can overcome the complexity issues involved in the implementation—and still plan effectively for site-wide disasters—you can create a solution that meets the needs of your organization and the bottom line as well.
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