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According to the National Institute of Standards and Technology (NIST), there are four approaches to achieving dependability: 1. Restoration is manual and can happen as soon as retrieval of tapes. [...] recently, this was probably the most common method of archival. 3.
Tips and Strategies for Systems Integrators | channel talk Fault tolerance and disaster recovery By Michael Whitt I n a perfect world, our control systems without an intolerable interruption in other documents. It is important to maintain would install and operate indeﬁnitely production even in the presence of these documents in order to quickly recon- with no faults. Experience teaches us ongoing hardware or software faults. struct sections of the facility if needed. otherwise. A Hot-Standby set of processors that Data security: This depends on a mix of Control system speciﬁcations should deal switch primaries upon fault detection automatic and manual processes. There with fault tolerance and failure recovery issues. would be an example of a fault toler- are two primary considerations for data A Hazard and Operability (HazOp) ant system, as would an Ethernet ring security in this context, backup and re- study is a good vehicle for determining topology that allows a device to fail store. Several of the more common op- the level of risk acceptable for a particular without interrupting the operation of tions for managing data follow. production process. If a formal HazOp is the remaining devices on the network. 1. No offsite data, daily backups to hard not practical, then it is up to the speciﬁca- 4. Fault evasion – Post-commissioning drive: This is the least secure. If the tion writer to do his own analysis. phase: Sense the trend toward a prob- computer fails, the backups are likely According to the National Institute of lem situation, and initiate corrective to be lost. The likelihood of being able Standards and Technology (NIST), there are action before the problem occurs. Set- to restore is remote. four approaches to achieving dependability: ting an alarm if network data through- 2. Daily backup to hard drive with a weekly 1. Fault avoidance – Design phase: Use put deviates beyond a set percentage backup to tape or other media. Onsite care to eliminate potential causes from the norm, giving the operator and offsite storage of tapes: This is bet- of faults in the design phase. This is time to make corrective action would ter. In this case, the most data that will where a HazOp or some other detailed be an example of fault evasion. be lost is a week. Restoration is manual method of analysis is most useful. The and can happen as soon as retrieval of HazOp process, when coupled with the Weighing failure recovery tapes. Until recently, this was probably proper application of industry standards Regardless of how bulletproof the design the most common method of archival. and accepted practices, followed by a is, how fault-tolerant the system, or how 3. Daily backup to hard drive with a weekly thorough design check, should help well trained the operators and technicians, backup to tape or other media. Onsite ﬁlter out most—but never all—of the system failures are still possible. Though and offsite storage of tapes. Redundant
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