VMFT - Primary-backup replication


  • system layers
    • Physical machine, OS/hypervisor, VM, OS/VM, Systems App, App
  • replication in different layers
    • e.g., replicating GFS master
  • virtual machine basics
    • a stream of instruction logs
    • inputs / outputs


  • pause, replicate states, continue (migration)
    • easy to implement
    • but cost time, can be used in adding new replica
  • state machine, replicate inputs
    • efficient in performance


  • Input events need to be replicated at exact point of instruction
  • When can primary return?
    • ack from F followers: tolerate F failures
    • otherwise?


  • clock
    • record
  • multi-core (different from multi-thread)
    • not supported in vmft
  • IO race
    • non-blocking
    • DMA

Input/Output consistency

  • exactly once over network? (TCP, UDP)
  • disk read

Network partition and “split-brain”

  • perfect failure detector? no
  • atomic test and set
  • can lease solve the problem?