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StarFish : highly-available block storage. 資訊三 李益昌 B00902051 資訊三 何柏勳 B00902097. Introduction. Data protection Disk failure V.S. catastrophic site failure Low price of disk drives and high-speed networking infrastructure StarFish Survive catastrophic site failure

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starfish highly available block storage

StarFish: highly-available block storage

資訊三李益昌B00902051

資訊三 何柏勳 B00902097

introduction
Introduction
  • Data protection
    • Disk failure V.S. catastrophic site failure
  • Low price of disk drives and high-speed networking infrastructure
  • StarFish
    • Survive catastrophic site failure
    • Use IP network : (1) geographically-dispersed (2) inexpensive
    • Good performance
    • Block level
architecture
Architecture
  • One Host Element(HE)
    • Provides storage virtualization and read cache
  • N Storage Element(SE)
    • Q: write quorum size.
    • Synchronous updates to a quorum of Q SEs, and asynchronous updates to the rest.
  • Communicate by TCP/IP over high speed network
architecture1
Architecture
  • Recommended configuration
    • N=3 Q=2
architecture2
Architecture
  • Another configuration
data consistency and se recovery
Data consistency and SE recovery
  • Log
    • sequential number
    • NVRAM
  • Data consistency
  • Failure
    • RAID or network connection fails
  • SE recovery
    • Quick recovery
    • Replay recovery
    • Full recovery
availability and reliability analysis
Availability and reliability analysis
  • Parameter
    • SE failure process :
    • SE recovery process :
    • Number of SEs : N
    • Quorum size : Q
  • Model
    • SEs failure process is i.i.d Poisson process with mean rate
    • SEs recovery process is i.i.d Poisson process with mean rate
    • HE failure process Poisson process with mean rate
    • HE recovery process Poisson process with mean rate
availability
Availability
  • a HE or SE is available if it can serve data
  • Availability of StarFish A(Q, N) : the steady-state probability that at least Q SEs are available
  • is called load ,
  • Repairman model
availability cont1
Availability(cont.)
  • SE availability = 1-
  • X★9:the number of 9s in an availability measure
  • Fixed N, availability decreases with large Q
    • Trade off availability for reliability
r eliability
Reliability
  • Probability of data loss
    • HE and Q SEs fails
  • The reliability increases with larger Q
  • Two approach
    • Q > floor(N/2) and at least Q SEs are available
      • Reduce availability
    • Read-only consistency
read only consistency
Read-only consistency
  • Available in read-only mode during failure.
    • Read-only mode obviates the need for Q SEs to be available to handle updates.
    • Increase availability
s etting
Setting
  • Gigabit Ethernet(GbE) with dummynet controlling delays and bandwith limit to model Internet links
  • Different network delays
    • 1, 2, 4, 8, 23, 36, 65 ms
  • Different bandwidth limitations
    • 31, 51, 62, 93, 124 Mb/s
  • Benchmark
    • Micro-benchmark
    • PostMark
effects of network delays and he cache size
Effects of network delays and HE cache size
  • Larger cache improves performance
  • Larger cache doesn’t change the response time of write requests
observation
Observation
  • Performance is affected by two parameters
    • Write quorum size Q
    • Delay to the SE
  • StarFish performs adequately when one of the SEs is placed in a remote location
    • At least 85% of the performance of a direct-attached RAID
recovery
Recovery
  • Performance degrades more during full recovery
c onclusion
Conclusion
  • The StarFish system reveals significant benefits from a third copy of data at an intermediate distance
  • A StarFish system with 3 replicas, a write quorum size of 2, and read-only consistency yields better than 99.9999% availability assuming individual Storage Element availability of 99%
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