Processors Toolkit

The seven Rs of high availability

Harris Kern Tech Republic

Published: 26 Nov 2002 13:06 GMT

The goal of all availability process owners is to maximise the uptime of the various online systems for which they are responsible -- in essence, to make them completely fault-tolerant. Constraints inside and outside the IT environment make this challenge close to impossible. Budget limitations, component failures, faulty code, human error, flawed design, natural disasters, and unforeseen business shifts such as mergers, downturns, and political changes are just some of the factors working against that elusive goal of 100 percent availability -- the ultimate expression of high availability.

There are several approaches the IT manager can take to maximise availability without breaking the budget bank. Each of these approaches start with the same letter, so I refer to them as the seven Rs of high availability. They are:

Redundancy
Reputation
Reliability
Repairability
Recoverability
Responsiveness
Robustness

Redundancy
Manufacturers have been designing redundancy into their products for years in the form of redundant power supplies, multiple processors, segmented memory, and redundant disks. This can also refer to entire server systems running in a hot standby mode. Infrastructure analysts can take a similar approach by configuring disk and tape controllers and servers with dual paths, splitting network loads over dual lines, and providing alternate control consoles -- in short, eliminating as much as possible any single points of failure that could disrupt service availability.

Reputation
The next three approaches -- reputation, reliability, and repairability -- are closely related. Reputation refers to the track record of key suppliers. Reliability pertains to the dependability of the components and the coding that go into their products. Repairability is a measure of how quickly and easily suppliers can fix or replace failing parts. We will look at each of these a bit more closely.

The reputation of key suppliers of servers, disk storage systems, database management systems, and network hardware and software plays a principle role in striving for high availability. It is always best to go with the best. You can verify reputations in several ways, including:

Percent of market share
Reports from industry analysts and Wall Street
Track record in the field
Customer references (these can be especially useful when it comes to confirming such factors as cost, service, quality of the product, training of service personnel, and trustworthiness)