Disconnected operation in the coda file system
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Disconnected Operation in the Coda File System. 姓名:吳佳憲 學號: 491516262. Outline. Motivation An Example Disconnected Operatio n Design Rationale Prioritized algorithm. Motivation. Disconnected Operation. Continue critical work when that repository is inaccessible. Key idea: caching data.

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Disconnected Operation in the Coda File System

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Disconnected operation in the coda file system

Disconnected Operation in the Coda File System

姓名:吳佳憲

學號:491516262


Outline

Outline

  • Motivation

  • An Example

  • Disconnected Operation

  • Design Rationale

  • Prioritized algorithm


Motivation

Motivation


Disconnected operation

Disconnected Operation

  • Continue critical work when that repository is inaccessible.

  • Key idea: caching data.

    • Performance

    • Availability

  • Server Replication


An example

An Example


An example1

An Example


An example2

An Example


An example3

An Example


An example4

An Example


An example5

An Example


Design rationale

Design Rationale

  • Scalability

    • Callback cache coherence (inherit from AFS)

    • Whole file caching

    • Fat clients. (security, integrity)

    • Avoid system-wide rapid change

  • Portable workstations

    • User’s assistance in cache management


Design rationale replication

Design Rationale -Replication

  • Server replication (why?)

    + Persistent, Secure physically

    - Expensive

  • Client replication

    - Low quality relatively

    +Cheap


Design rationale replica control

Design Rationale –Replica Control

  • Pessimistic

    • Disable all partitioned writes

      - Require a client to acquire control of a cached object prior to disconnection

  • Optimistic

    • Assuming no others touching the file

    • sophisticated: conflict detection

      + fact: low write-sharing in Unix

      + high availability: access anything in range


Implementation architecture

Implementation - architecture


Venus states

Venus - states


Hoarding

Hoarding

  • Hoard useful data for disconnection

  • Balance the needs of connected and disconnected operation.

    • Cache size is restricted

    • Unpredictable disconnections

  • Prioritized algorithm – cache manage

  • hoard walking – reevaluate objects


Prioritized algorithm

Prioritized algorithm

  • User defined hoard priority p: how interest it is?

  • Recent Usage q

  • Object priority = f(p,q)

  • Kick out the one with lowest priority

    + Fully tunable

    Everything can be customized

    - Not tunable (?)

    • No idea how to customize


Hoard walking

Hoard Walking

  • Equilibrium – uncached obj < cached obj

    • Why it may be broken? Cache size is limited.

  • Walking: restore equilibrium

    • Reloading HDB (changed by others)

    • Reevaluate priorities in HDB and cache

    • Enhanced callback

  • Increase scalability, and availability

  • Decrease consistency


Emulation

Emulation

  • Act like a server

  • Record modified objects

  • Replay update activity Preparation

    • Log based per volume

  • Persistence

    • Meta-data  RVM

    • Exhaustion

      • Compress?


Conflict handling

Conflict Handling

  • Only care write/write confliction

  • File vs Directory

    • File: Halt entire reintegration process

    • Dir: investigate more

    • Manual repair


Conclusion

Conclusion

  • Doda is DFS with support for disconnected operation


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