Where is anti-virus software typically installed?

• malignant viruses • propagation engine • scripting hosts • self-replicating • shell • signature • virus scanner • worms

Chapter 9: Creating Fault Tolerance

Overview Security means more than just keeping hackers out of your computers. It really means keeping your data safe from loss of any kind, including accidental loss due to user error, bugs in software, and hardware failure. Systems that can tolerate hardware and software failure without losing data are said to be fault tolerant. The term is usually applied to systems that can remain functional when hardware or software errors occur, but the concept of fault tolerance can include data backup and archiving systems that keep redundant copies of information to ensure that the information isnt lost if the hardware it is stored upon fails. Fault tolerance theory is simple: Duplicate every component that could be subject to failure. From this simple theory springs very complex solutions, like backup systems that duplicate all the data stored in an enterprise, clustered servers that can take over for one another automatically, redundant disk arrays that can tolerate the failure of a disk in the pack without going offline, and network protocols that can automatically reroute traffic to an entirely different city in the event that an Internet circuit fails. Causes for Loss To correctly plan for fault tolerance, you should consider what types of loss are likely to occur. Different types of loss require different fault tolerance measures, and not all types of loss are likely to occur to all clients. fault tolerance The ability of a system to withstand failure and remain operational. At the end of each of these sections, there will be a tip box that lists the fault tolerance measures that can effectively mitigate these causes for loss. To create an effective fault tolerance policy, rank the following causes for loss in the order that you think they’re likely to occur in your system. Then list the effective remedy measures for those causes for loss in the same order, and implement those remedies in top-down order until you exhaust your budget. Note The solutions mentioned in this section are covered in the second half of this chapter.