Cost Tradeoff of Consistency Over Data Centers Ozlem Bilgir

Outline Problem What do we need to solve the problem? What is Consistency? General Formulation Solution Approaches Results

Source: EPA Report to Congress on Server and Data Center Energy Efficiency What is the Problem? In 2006, data centers in US consumed ~60billion KWhs I.Cost : In 2006, total data center electricity cost in US was $4.5billion II.Greenhouse Gases : In 2008, data centers caused more carbon emissions than Argentina &Netherland (Source: McKinsey & Company, 2008)

What Do We Need? Good way of request distribution : to minimize cost Brown Energy Caps: to limit the brown energy consumption at data centers Satisfy SLA Don’t overload any of the data center Satisfy consistency over replicas

What is Consistency? Data are not stored only in one data center 3 types of consistency; – Weak Consistency: ex. VOiP – Eventual Consistency: ex. – Strong Consistency: ex. File upload

General Formulation

Assumptions 3 data center -- They are all replicas of each other All data centers can serve all types of requests Strong consistency over data centers Data centers consume same energy to process all types of requests

Solution Approaches Simulated Annealing: To solve optimization problem CA-Heuristic : – Sort the data centers according to Cost i (t)/CDF i (L;LCi) ratio, – send to first one until it overloads, – send to next ones until SLA satisfies, – send to cheapest one CU-Heuristic : Don’t take cost into account

Results

Conclusion Extra cost from consistency is added to the general cost Future Work: Back to the Control Theory!!!