Editor's note: DM Review welcomes new columnists David Wegman and George Loechl. In their Managed Availability Memo column, they will share their expertise on managed availability issues, including availability solution development and design relative to the availability continuum.

Ask a group of 10 IT managers, DBAs and CIOs to define system availability or high availability and you are likely to get 10 different answers. That's because data and applications availability, as a business requirement, parallels the rapid evolution of technology - and just when we think we've got things pinned down, they start changing again.

Never before have information assets been so critical in leveraging competitive advantage, contributing to profitability and sustaining business viability. Undoubtedly, the growing importance of information availability is the byproduct of a mega change in data accumulation and how it is processed, accessed, shared and transformed in certain environments. A few key elements of this tide of change include:

  • The evolution from highly centralized computing, in which a limited number of computers and individuals provided the information needs of an organization, to a highly diversified approach, whereby huge databases might be centrally managed but processing is spread throughout the nodes of a networked or clustered enterprise, providing users the applications and information they need to manipulate and share data while benefiting from browser-based technology.
  • The creation of what some analysts call "data smog," an incredible explosion of information reflected in the current worldwide production of between two and four exabytes of brand-new data annually. This equates to more than 400 megabytes for every man, woman and child on the planet.
  • The conversion of business applications and activities, such as e-mail, from workplace conveniences to critical dependencies that anchor information sharing and integration.
  • The increasing complexity and interdependency of both hardware and software architectures characterized by various best-of-breed and legacy applications interfacing across multiple platforms and with heterogeneous databases, increasing the risk in component failure.
  • The emergence of the 24x7 business day in response to expanding worldwide commerce, diversified supply chains, non-stop production and e-business practices.

The accelerating, technology-driven tide of change and the various stages of growth through which an organization passes constantly reshape our understanding of availability requirements. The result is that managed availability - the ability of an organization to deliver consistent, predictable access to information for any user wherever, whenever and however they need it - is not a static business discipline but one that must be defined by solution flexibility and scalability as well as by variable tolerance for planned and unplanned downtime.

As we examine the issues, a deeper understanding of managed availability is required. This begins with an assessment of "where you are" on an availability continuum - a measure that progresses from reactive to business requirements to a posture that is far more proactive to business requirements.

The availability continuum graphic in Figure 1 shows the relativity of various availability protocols and their associated executions.

Figure 1

Disaster Recovery (DR), at the bottom-left corner of the continuum, emphasizes data recovery over applications recovery. Levels of DR, usually expressed in the time it takes to recover data and certain system components, may vary considerably, because the required level of DR depends on the data sensitivities and, to a lesser extent, the operational needs of an organization. Data-priority DR is primarily a defensive action offering limited, but specific, resiliency; therefore, it is said to be "reactive to business requirements."

Improved Availability (IA) and High Availability (HA) are the next reference points as we move to the right and upward along the continuum. True HA assigns priority to applications availability and assumes high data availability because, in this circumstance, the operational needs of an organization take precedence over data sensitivities because the data is assumed to be there. With applications-priority HA, the time it takes to recover certain system components may be significantly shorter than in many DR scenarios.

The myriad permutations of contemporary computing environments, as well as a host of availability solution options with varying power and functionality, have recently induced analysts to introduce the reference point of IA. The difference between HA and IA is determined by the degree to which a solution is leaning towards the limited resiliency of "reactive" DR or leaning towards the initiative-centric resiliency of "proactive" continuous availability.

Continuous Availability (CA), or continuous operations, at the far upper-right of the continuum, is the highest order of system resiliency. With CA, the operational needs and data sensitivities of an organization are both considered top tier. Our solution stance has become so "proactive driven" that applications and data - holistically understood as information critical to the enterprise - are of equal priority. CA enables seamless, 24x7 system availability that offsets any planned or unplanned downtime event.

Robust CA is most commonly achieved through the integration of many aspects of an enterprise. Such aspects include methods, skills, highly reliable hardware and advanced-function replication software, which not only maintains a mirrored image of production on a backup server, but also facilitates seamless switching of the production environment to the backup server so that system activities associated with planned downtime can be easily initiated and completed without disrupting enterprise operations.

As we move from the hypothetical to the practical, it is important to note there are many variations of solutions in between the two extremes of the top right and bottom left of our availability continuum. For each user, the choice of a specific availability solution is influenced by what fits the present needs of the business, the planned growth, the degree by which the business needs may evolve and how well the chosen solution can be cost-justified.

In our next "Managed Availability Memo," we will discuss the difference between recovery point objective (RPO) and recovery time objective (RTO), terms that help us establish benchmark requirements in availability planning and help define "where you are" on the availability continuum.

DM Review online readers who wish to study managed availability issues and technology in greater depth may subscribe to Vision Solutions' Business Continuity Series at www.visionsolutions.com/BCSS.

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