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Impact of Layering and Faults on Availability and its End-to-End Implications

Impact of Layering and Faults on Availability and its End-to-End Implications. Ricardo Bianchini, Richard Martin , Thu Nguyen Department of Computer Science Rutgers University. Application. Language VM. OS VM. Virtual FS. FS. Virtual Disk. SCSI. IDE. Layers on Layers on Layers.

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Impact of Layering and Faults on Availability and its End-to-End Implications

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  1. Impact of Layering and Faults on Availabilityand its End-to-End Implications Ricardo Bianchini, Richard Martin, Thu Nguyen Department of Computer Science Rutgers University Computer Science, Rutgers University

  2. Application Language VM OS VM Virtual FS FS Virtual Disk SCSI IDE Layers on Layers on Layers Operating System Socket TCP IP Enet WiFi Computer Science, Rutgers University

  3. Clients IP Network Load Manager Web Server Web Server Web Server DataBase DataBase Global Layering Tier 1 Tier 2 Tier 3 Computer Science, Rutgers University

  4. Availability • Correct response within accepted time bound • Fraction correct/90th percentile response time • Two components: • Correctness • Time bound • To get to 99.999 nines (5 min unavailability/year) • Not a lot of time to mess around Computer Science, Rutgers University

  5. Clients IP Network Load Manager Web Server Web Server Web Server DataBase DataBase 2 Second Reponse time Tier 1 Tier 2 Tier 3 Computer Science, Rutgers University

  6. Application Language VM OS VM Virtual FS FS Virtual Disk SCSI Impact of Faults and Layers • Each layer built independently • Intermediate layers hide exceptional conditions • Buffer and continue • Retry N • Crashes • Punt • Hard to build availabile systems • React quickly enough? • Diagnosis difficult • Prediction try { do_stuff(); }catch(e) { freak_out(); } Fault Computer Science, Rutgers University

  7. End-to-End Implications • Traditional Philosophy • End-to-end checks necessary for correctness, • Intermediate checks only a performance enhancement • Availability oriented: • End-to-end checks necessary for correctness • Intermediate checks and timely cross-layer propagation of information necessary • How to achieve these properties while maintaining layering? Computer Science, Rutgers University

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