The document discusses different replication strategies for cloud storage to reduce data loss. Copyset replication groups storage nodes into sets where each set stores the same data. This reduces correlated failures compared to random replication. Tuning the scatter width, which is the number of sets per data item, controls the parallelism of data recovery from node failures. Wider scatter widths result in lower recovery loads on individual nodes but increase the chance of data loss. The strategies aim to minimize both the frequency and amount of data lost from node failures in cloud storage systems.

1. opysets:
Reducing the Frequency of Data Loss
in Cloud Storage
Aysylu Greenberg
Papers We Love Denver
April 27, 2017

2. Welcome Papers We Love Denver!

3. Aysylu Greenberg
@aysylu22
paperswelove.org

5. Today
• Random replication
• Copyset Replication
• Copyset Replication with Scatter Width
• Pragmatic aspects

6. RANDOM REPLICATION
Overview & Tradeoffs

7. Random Replication
R = 3
N = 9

8. Random Replication:
Correlated Failures

9. Recovery from Data Loss
Fixed cost of restoring lost data is high
Lose more data but less often
Increase in R is expensive

10. Random Replication:
Tradeoff
{small amount &
high frequency}
data loss
{large amount &
low frequency}
data loss

11. COPYSET REPLICATION
Intuition

12. Copyset Replication
R = 3
N = 9

13. Copyset Replication
R = 3
N = 9
S = 2

14. Recovery from Node Failure
Simpler recovery than random replication:
R – 1 nodes with data
Higher load on small number of nodes

15. Copyset Replication with S = 2:
Tradeoff
{small amount &
high frequency}
data loss
{large amount &
low frequency}
data loss

16. SCATTER WIDTH
Tuning choices

17. Copyset Replication with S=2
R = 3
N = 9

18. Copyset Replication with S=4
R = 3
N = 9

19. Copyset Replication with S = 4
1 2 3
654
7 8 9 R = 3
N = 9

20. 1 2 3
654
7 8 9
1 2 3
654
7 8 9
Copyset Replication with S = 4:
Permutation Phase

21. 1 2 3
654
7 8 9
Copyset Replication with S = 4:
Permutation Phase

22. 1 2 3
654
7 8 9
Copyset Replication with S = 4:
Permutation Phase

23. 1 2 3
654
7 8 9
Copyset Replication with S = 4:
Permutation Phase

24. Tuning Scatter Width
Set by system designer to control parallelism
of data recovery
Control load on each individual node during
recovery

25. Copyset Replication Scatter Width:
Tradeoffs
{small amount &
high frequency}
data loss
{large amount &
low frequency}
data loss

26. Scatter Width:
Tuning Choices
Random replication: scatter width of N-1, lots
of replica sets

27. Scatter Width:
Tuning Choices
Random replication: scatter width of N-1, lots
of replica sets
S << N

28. Scatter Width:
Tuning Choices
Random replication: scatter width of N-1, lots
of replica sets
S << N
To reduce frequency of data loss, minimize:

29. FROM IDEAS TO PRACTICE
Pragmatic aspects

30. Pragmatic Aspects
• Move randomization to permutation stage
• Low overhead on operations
• Near optimal and fast
• Support for dynamic systems while
maintaining guarantees is tricky -> chainsets
(http://hackingdistributed.com/2014/02/14/chainsets/)
• Tiered
replicationhttps://www.usenix.org/conference/atc15/t
echnical-session/presentation/cidon

31. opysets:
Reducing the Frequency of Data Loss
in Cloud Storage
Aysylu Greenberg
Papers We Love Denver
April 27, 2017