Understanding the Availability Levels

By Tom Reed  |  Posted 2009-11-13 Print this article Print

Understanding the availability levels

There are multiple levels of availability to consider for different applications and their support infrastructures. The levels of availability start with basic failover and recovery, move up to high availability (HA), and go all the way to continuous availability for extremely transaction-sensitive applications. Let's take a closer look at each level:

Level No. 1: The recovery level

The recovery level is for those applications for which a RTO of a day or more is often acceptable. Some downtime is acceptable and even significant downtime won't have a detrimental effect on the business. Assurances that recovery will happen is not a requirement.

Level No. 2: The HA level

The HA level is the home of the majority of applications that run the business such as e-mail, CRM, financial systems and databases. These are systems with high downtime costs and therefore short RTO requirements. These applications require assurances that they will not be down for extended periods should failures occur.

Level No. 3: The continuous availability level

The highest level of availability is continuous availability, in which even brief moments of downtime or a single lost transaction can be extremely detrimental and/or costly to the client or business.

As you establish availability objectives for different groups of Exchange users, you need to consider the protection requirements for your entire Exchange infrastructure, beyond just the mailbox server. You will need to protect all of the components of the Exchange environment, in addition to the different workloads deployed on the mailbox server.

Also, don't rule out the possibility that the way you use Exchange today may change in the future. You may use Exchange today for general correspondence but within the next year you may plan to use e-mail to process orders. This adds to the need to have multiple levels of availability to assign to the components of the Exchange infrastructure and Exchange user groups. Additionally, you'll need flexibility to change those levels as your business changes.

Tom Reed is Senior Solutions Architect at Marathon Technologies Corporation, where he is responsible for the deployment of mission-critical platforms to support enterprise-computing environments. He can be reached at treed@marathontechnologies.com.

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