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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

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

layers on layers on layers

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

global layering

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

availability
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

2 second reponse time

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

impact of faults and layers

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

end to end implications
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