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

4.
Today
• Random replication
• Copyset Replication
• Copyset Replication with Scatter Width
• Pragmatic aspects

5.
RANDOM REPLICATION
Overview & Tradeoffs

6.
Random Replication
R = 3
N = 9

7.
Random Replication:
Correlated Failures

8.
Recovery from Data Loss
Fixed cost of restoring lost data is high
Lose more data but less often
Increase in R is expensive

9.
Random Replication:
Tradeoff
{small amount &
high frequency}
data loss
{large amount &
low frequency}
data loss

10.
COPYSET REPLICATION
Intuition

11.
Copyset Replication
R = 3
N = 9

12.
Copyset Replication
R = 3
N = 9
S = 2

13.
Recovery from Node Failure
Simpler recovery than random replication:
R – 1 nodes with data
Higher load on small number of nodes

14.
Copyset Replication with S = 2:
Tradeoff
{small amount &
high frequency}
data loss
{large amount &
low frequency}
data loss

15.
SCATTER WIDTH
Tuning choices

16.
Copyset Replication with S=2
R = 3
N = 9

17.
Copyset Replication with S=4
R = 3
N = 9

18.
Copyset Replication with S = 4
1 2 3
654
7 8 9 R = 3
N = 9

19.
1 2 3
654
7 8 9
1 2 3
654
7 8 9
Copyset Replication with S = 4:
Permutation Phase

20.
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.
Tuning Scatter Width
Set by system designer to control parallelism
of data recovery
Control load on each individual node during
recovery

24.
Copyset Replication Scatter Width:
Tradeoffs
{small amount &
high frequency}
data loss
{large amount &
low frequency}
data loss

25.
Scatter Width:
Tuning Choices
Random replication: scatter width of N-1, lots
of replica sets

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

27.
Scatter Width:
Tuning Choices
Random replication: scatter width of N-1, lots
of replica sets
S << N
To reduce frequency of data loss, minimize:

28.
FROM IDEAS TO PRACTICE
Pragmatic aspects

29.
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

30.
opysets:
Reducing the Frequency of Data Loss
in Cloud Storage
Aysylu Greenberg
Papers We Love Denver
April 27, 2017