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Power efficiency is one of the main issues that will drive the design of data centers, especially of those devoted to provide Cloud computing services. In virtualized data centers, consolidation of Virtual Machines (VMs) on the minimum number of physical servers has been recognized as a very efficient approach, as this allows unloaded servers to be switched off or used to accommodate more load, which is clearly a cheaper alternative to buy more resources. The consolidation problem must be solved on multiple dimensions, since in modern data centers CPU is not the only critical resource: depending on the characteristics of the workload other resources, for example, RAM and bandwidth, can become the bottleneck. The problem is so complex that centralized and deterministic solutions are practically useless in large data centers with hundreds or thousands of servers. This paper presents ecoCloud, a selforganizing and adaptive approach for the consolidation of VMs on two resources, namely CPU and RAM. Decisions on the assignment and migration of VMs are driven by probabilistic processes and are based exclusively on local information, which makes the approach very simple to implement. Both a fluid-like mathematical model and experiments on a real data center show that the approach rapidly consolidates the workload, and CPU-bound and RAM-bound VMs are balanced, so that both resources are exploited efficiently.


In the past few years important results have been achieved in terms of energy consumption reduction, especially by improving the efficiency of cooling and power supplying facilities in data centers. The Power Usage Effectiveness (PUE) index, defined as the ratio of the overall power entering the data center and the power devoted to computing facilities, had typical values between 2 and 3 only a few years ago, while now big Cloud companies have reached values lower than 1.1. However, much space remains for the optimization of the computing facilities themselves. It has been estimated that most of the time servers operate at 10-50 percent of their full capacity [2], [3]. This low utilization is also caused by the intrinsic variability of VMs’ workload: the data center is planned to sustain the peaks of load, while for long periods of time (for example, during nights and weekends), the load is much lower [4], [5]. Since an active but idle server consumes between 50 and 70 percent of the power consumed when it is fully utilized [6], a large amount of energy is used even at low utilization.


  • It is power consuming.
  • Large amount of energy is used even at low utilization.


The ever increasing demand for computing resources has led companies and resource providers to build large warehouse-sized data centers, which require a significant amount of power to be operated and hence consume a lot of energy.


The optimal assignment of VM’s to reduce the power consumption.


We presented ecoCloud, an approach for consolidating VMs on a single computing resource, i.e., the CPU. Here, the approach is extended to the multidimension problem, and is presented for the specific case in which VMs are consolidated with respect to two resources: CPU and RAM. With ecoCloud, VMs are consolidated using two types of probabilistic procedures, for the assignment and the migration of VMs. Both procedures aim at increasing the utilization of servers and consolidating the workload dynamically, with the twofold objective of saving electrical costs and respecting the Service Level Agreements stipulated with users. All this is done by demanding the key decisions to single servers, while the data center manager is only requested to properly combine such local decisions. The approach is partly inspired by the ant algorithms used first by Deneubourg et al. [9], and subsequently by a wide research community, to model the behavior of ant colonies and solve many complex distributed problems. The characteristics inherited by such algorithms make ecoCloud novel and different from other solutions. Among such characteristics: 1) the use of the swarm intelligence paradigm, which allows a complex problem to be solved by combining simple operations performed by many autonomous actors (the single servers in our case); 2) the use of probabilistic procedures, inspired by those that model the operations of real ants; and 3) the self-organizing behavior of system, which ensures that the assignment of VMs to servers dynamically adapts to the varying workload.


  • Efficient CPU usage.
  • It reduces power consumption.
  • Efficient resource utilization.


Distributed, Concurrent, And Independent Access To Encrypted Cloud Databases



Processor                  -        Pentium –IV

Speed                        -        1.1 Ghz

RAM                         -        512 MB(min)

Hard Disk                 -        40 GB

Key Board                -        Standard Windows Keyboard

Mouse                       -        Two or Three Button Mouse

Monitor                     -        LCD/LED


  • Operating system       :         Windows XP
  • Coding Language        :         Java
  • Data Base                        :         MySQL
  • Tool                                  :         Net Beans IDE


Luca Ferretti, Michele Colajanni, and Mirco Marchetti“Distributed, concurrent, and independent access to encrypted cloud databases” VOL. 25, NO. 2, FEBRUARY 2014.

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