f33-book-depend-pres-pt6

f33-book-depend-pres-pt6 - Nov. 2009 Part VI Degradations:...

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Nov. 2009 Part VI – Degradations: Behavioral Lapses Slide 1
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Nov. 2009 Part VI – Degradations: Behavioral Lapses Slide 2 About This Presentation This presentation is intended to support the use of the textbook Dependable Computing: A Multilevel Approach (traditional print or on-line open publication, TBD). It is updated regularly by the author as part of his teaching of the graduate course ECE 257A, Fault-Tolerant Computing, at Univ. of California, Santa Barbara. Instructors can use these slides freely in classroom teaching or for other educational purposes. Unauthorized uses, including distribution for profit, are strictly prohibited. © Behrooz Parhami Edition Released Revised Revised Revised Revised First Sep. 2006 Oct. 2007 Nov. 2009
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Nov. 2009 Part VI – Degradations: Behavioral Lapses Slide 3 21 Degradation Allowance
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Nov. 2009 Part VI – Degradations: Behavioral Lapses Slide 4 Our computers are down, so we have to do everything manually. .. “Redundancy is such an ugly word. Let’s talk about your ‘employment crunch’.”
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Nov. 2009 Part VI – Degradations: Behavioral Lapses Slide 5 Robust Parallel Processing Resilient Algorithms
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Nov. 2009 Part VI – Degradations: Behavioral Lapses Slide 6 21.1 Graceful Degradation Degradation allowance Diagnose malfunctions and provide capability for the system to work without the modules which are malfunctioning Degradation management Adapt: Prioritize tasks and redistribute load Monitor: Keep tack of system operation in degraded mode Reverse: Return system to the intact (or less degraded) state ASAP Return: Go back to normal operation Terminology: n. Graceful degradation adj. Gracefully degrading/degradable = fail-soft Strategies for failure prevention 1. Quick malfunction diagnosis 2. Effective isolation of malfunctioning elements 3. On-line repair (preferably via hot-pluggable modules) 4. Avoidance of catastrophic malfunctions
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Nov. 2009 Part VI – Degradations: Behavioral Lapses Slide 7 Area under performance curve represents work accomplished Off-line repair On-line repair Performability of a Fail-Soft System On-line repair: Done by removal/replacement of affected modules in a way that does not disrupt the operation of the remaining system parts Crashed Off-line repair: Involves shutting down the entire system while affected modules are removed and replacements are plugged in Intact Time Fail-soft operation Degraded Partially failed Performance
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Nov. 2009 Part VI – Degradations: Behavioral Lapses Slide 8 21.2 Diagnosis, Isolation, and Repair Diagnose the malfunction Remove the malfunctioning unit Update system (OS) tables Physical isolation? Initiate repair, if applicable Create new working configuration Exclude processor, channel, controller, I/O device (e.g., sensor) Avoid bad tracks on disk, garbled files, noisy communication links Remove parts of the memory via virtual address mapping Bypass a cache or use only half of it (more restricted mapping?) Unit Guard 1 Bus Guard 2 Recover processes and associated data Recover state information from removed unit Initialize any new resource brought on-line Reactivate processes (via rollback or restart) Additional steps needed to return repaired units to operating status
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Nov. 2009
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f33-book-depend-pres-pt6 - Nov. 2009 Part VI Degradations:...

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