Starfish highly available block storage
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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

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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 cont

Availability(cont.)


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


Availability with read only consistency

Availability with Read-only Consistency


Implementation

Implementation


Performance measurements

Performance measurements


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


Normal operation and placement of the far se

Normal Operation and placement of the far SE


Normal operation and placement of the far se1

Normal Operation and placement of the far SE


Normal operation and placement of the far se2

Normal Operation and placement of the far SE


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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