A451 - 1.1: The Need for Reliability

What is Reliability?
1. When you are confident that they will do what is expected of them
Effect of Failure
1. Personal Effect: Work lost, photographs lost etc.
2. Failure in a Business: e.g. A Building Society loses the mortgages managed as a flood/fire breaks out into the data centre. Is this acceptable? This could destroy the company
Redundancy
1. It is a method of improving reliability
2. It means that critical parts of the system are duplicated so if a failure occurs, the other sub-system can take over
3. e.g. Power supply may be duplicated. If the power begins to diminish, the other power supply kicks in.
Data Redundancy
1. To duplicate the data in more than once place within a computer system
2. It can be done by having two or more hard disks running in parallel and storing the same data.
3. If one fails, the other still works, no data is lost. The broken disk is then swapped out for a new one.
Software Redundancy
1. More rare, but still used for critical programs which cannot afford to fail
2. The ideas is to have 3 software routines, each written by different coding teams, producing the same output if given the same input
3. The computer uses a kind of voting system, and determines if one is not getting the correct output, highlighting a bug in one of the codes.
Backing Up
1. Single Machines: It's a good idea to backup to an external hard drive.
2. Network Server: Back up to digital tape machines replicating data of the remote server
3. Data Centre: Large organisation may have backed up far, far away. So a fire/flood in the main centre won't destroy the backup
4. Cloud: Cloud Backup, Backup to the cloud duuhhhhhhhhhhhhhhh

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A451 - 1.1: The Need for Reliability

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