1. Value of Non-functional
Qualities of Cloud Storage
First Thoughts / Brain Teaser

2. Retrospective
started with Cassandra and consistency trade-offs
cost for higher consistency level is costs of additional servers
ended up juggling with throughput, latency +
consistency level

3. Why determine the value of non-fct.ies?
}
measuring non-fct. qualities
e.g. David's consistency benchmark, YCSB
Ho to derive an
modifying non-fct. qualities optimal setup?
e.g. Markus & Michael's storage tuning
non-fct. qualities: e.g. consistency, throughput, latency

4. Focus
Focus on 3 important non-fct. properties of Cloud storage:
latency
throughput
consistency

5. Latency effect
waiting for a response
measurable
in time units

6. Throughput effect
full server, no response
measurable
in % success
HTTP 503 Error

7. Consistency effect
server-side inconsistencies until eventually...
access to stale server
inconsistency window
measurable in multiple metrics
in time units inconsistency window,
in size of (numerical, version) difference
!!! server-side inconsistency can be covered by
mechanisms, e.g. read repair -> effort!

8. Influence on non-fct. qualities
1. parameters can be modified in Cloud storage
2. non-fct. qualities react on parameter changes
3. every parameter setting results in (l, t, c) outcome
= (l, t, c)

9. Determine Optimal Value
measure parameter settings for (l, t, c) outcomes
generate value-outcome map: (l, t, c) -> value
find optimal value in value-outcome map
parameter optimization:
Songyun Duan, Vamsidhar Thummala, and Shivnath Babu. 2009. Tuning database
configuration parameters with iTuned. Proc. VLDB Endow. 2, 1 (August 2009),
1246-1257.

10. How to find the value? A formula?

11. Mind:
Qualities do not fully compensate!
There are min/max limits for non-fct. qualities!
There might be settings where 2 qualities are high!
Evaluation formula must consider
that!

12. Determine the value of non-fct. qualities!
measuring non-fct. qualities
e.g. David's consistency benchmark
}
modifying non-fct. qualities
everything
e.g. Markus & Michael's storage tuning perfect?
optimize non-fct. qualities
assuming a formula is defined

13. No meaning without business context!
Finding appropriate formula:
Without understanding business impacts weights are arbitrary!
1. Consider the business case!
e.g. e-business case (immediate impact on business)
2. Insert actual costs into formula!
costs of latency, incosistencies, ...
What are the costs?

14. Effects of (l, t, c) in e-business context
... become more specific!
e-business case: online shop
latency
patience, 4 sec rule [1]
throughput
no response, lost sale
consistency
misinformation, over-sell
[1] Jupiter Research (2006), Retail Web Site Performance: Consumer Reaction to a Poor Online Shopping
Experience, Vendor Research commissioned by Akamai. (http://www.akamai.com/4seconds).

15. A formula in e-business context

16. Requirements for approach
1. Probabilities must be determined.
Big Tasks!
2. Costs/benefits must be determined.
3. Cost/Benefit relations must be expressed in a formula.
or use standard formula?

17. Outlook/Open Questions
Right indicators/metrics measured?
Throughput, Latency and Consistency are of great interest.
Can cost/prices always be determined?
A business should know.
The perfect formula?
No, only fair formula and model that helps making a decision.

18. One step further...
self-optimizing Cloud storage
that minimizes business risks and benefits
according to the user's parameters

19. Thank You!
Questions / Discussion...

20. Contact Me
For Questions, Discussions,
or Initiating Research Exchange:
Michael Menzel
Research Center for Information Technology (FZI)
Karlsruhe Institute of Technology (KIT)
Englerstr. 11
76131 Karlsruhe
Email: menzel@fzi.de