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A451 - 1.1: The Need for Reliability
- What is Reliability?
- When you are confident that they will do what is expected of them
- When you are confident that they will do what is expected of them
- Effect of Failure
- Personal Effect: Work lost, photographs lost etc.
- 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
- Personal Effect: Work lost, photographs lost etc.
- Redundancy
- It is a method of improving reliability
- It means that critical parts of the system are duplicated so if a failure occurs,
the other sub-system can take over
- e.g. Power supply may be duplicated. If the power begins to diminish,
the other power supply kicks in.
- It is a method of improving reliability
- Data Redundancy
- To duplicate the data in more than once place
within a computer system
- It can be done by having two or more hard disks running in parallel and storing the same data.
- If one fails, the other still works, no data is lost. The
broken disk is then swapped out for a new one.
- To duplicate the data in more than once place
within a computer system
- Software Redundancy
- More rare, but still used for critical programs which cannot afford to fail
- The ideas is to have 3 software routines, each written by different coding
teams, producing the same output if given the same input
- 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.
- More rare, but still used for critical programs which cannot afford to fail
- Backing Up
- Single Machines: It's a good idea to backup to an external hard drive.
- Network Server: Back up to digital tape machines
replicating data of the remote server
- Data Centre: Large organisation may have backed up far, far away. So a
fire/flood in the main centre won't destroy the backup
- Cloud: Cloud Backup, Backup to the cloud duuhhhhhhhhhhhhhhh
- Single Machines: It's a good idea to backup to an external hard drive.
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