| Can you see what's coming next? What
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| | capabilities in the software, usually the
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| happens if the controller fails? Ha! -
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| | operating system.The software is set up
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| we're ready for that! We put in another
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| | to take note of errors detected by the
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| controller, and connect the second string
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| | hardware, and automatically 'mark down' a
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| of cables to this one instead! Redundant
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| | specific component, or access path,
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| controllers.Other configurations are also
| |
| | depending on a preset 'threshold' of
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| possible, using both interfaces on both
| |
| | error tolerance. At the same time, the
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| controllers, however these are mainly
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| | system operations and maintenance
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| concerned with system throughput, or the
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| | personnel are alerted, so that the
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| ability to switch drives between two or
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| | perceived problem can be rectified.The
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| more systems. The extra redundancy
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| | provision of redundancy in a system gives
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| provided in these cases is more of a
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| | the maintenance engineer the ability to
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| bonus than a necessity.Moving further up
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| | work on the failing component or path
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| the data chain, we need a path between
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| | while the system continues operation. We
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| the controller and the I/O (input/output)
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| | can also test multiple paths to a
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| section of the mainframe. By now you
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| | component to eliminate possible causes of
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| will see that we will use two paths to
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| | a failure which, we have seen, could lie
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| provide redundancy. You can also work
| |
| | anywhere in the chain from the drive back
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| out that, if the I/O unit fails, we have
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| | to the I/O unit.A further redundancy
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| problems, not only in talking to our disk
| |
| | commonly built in to large systems is
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| drive but to tapes, printers, datacomms
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| | the power supply. The system power is
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| etc.This possibility of any one component
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| | provided by a generator, driven by a
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| in the system being able to affect the
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| | motor, which is driven from mains power.
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| whole system, or a significant section of
| |
| | In the event of a power supply failure, a
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| it, is known as 'Single Point
| |
| | diesel engine takes over driving the
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| Sensitivity'. A Single Point of Failure
| |
| | generator to ensure continuous power.
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| is one which has the potential to affect
| |
| | The change-over period is covered by
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| operations to some extent.The way to
| |
| | batteries, which are kept charged during
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| avoid this, of course, is to duplicate
| |
| | normal operation. In another version,
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| everything, CPUs, I/Os, Controls etc.
| |
| | the batteries drive the generator and
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| The most difficult component to duplicate
| |
| | isolate the system from power surges.The
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| is memory, as this is the basic part of
| |
| | complete system can be duplicated in this
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| the system, where everything is
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| | way, with more resources being placed in
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| controlled.Multi processors have been in
| |
| | susceptible areas, such as disks and
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| operation since the 1960s and dual paths
| |
| | tapes. The cost of additional components
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| have been used to access subsystems. In
| |
| | is weighed against the requirement for
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| the case of larger systems, for example a
| |
| | continuous operation, and what effect a
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| 6x4 (6 CPUs, 4I/Os) for paths were
| |
| | catastrophic failure might have. The
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| provided to disk and tape controllers to
| |
| | ultimate redundancy uses a completely
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| increase throughput and allow 2 or more
| |
| | separate duplicate system located at a
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| operating systems to run on selected
| |
| | remote area, possibly hundreds of miles
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| components. Units can be combined or
| |
| | distant (of course, with duplicated
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| removed 'on the fly' and systems carry on
| |
| | links!)Tony is an experienced computer
|
| working with more or less resources.We
| |
| | engineer. He is currently webmaster and
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| have talked about redundancy in hardware,
| |
| | contributor to . A set of diagrams
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| or the physical components of the system,
| |
| | accompanying these articles may be seen
|
| by providing alternative hardware. There
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| | at .
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| is also the provision of redundant
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| |
|
