Saber, TakfarinasTakfarinasSaberThorburn, JamesJamesThorburnMurphy, Liam, B.E.Liam, B.E.MurphyVentresque, AnthonyAnthonyVentresque2017-11-132017 Elsev2017Future Generation Computer Systemshttp://hdl.handle.net/10197/9041Optimising the data centres of large IT organisations is complex as (i) they are composed of various hosting departments with their own preferences and (ii) reassignment solutions can be evaluated from various independent dimensions. But in reality, the problem is even more challenging as companies can now choose from a pool of cloud services to host some of their workloads. This hybrid search space seems intractable, as each workload placement decision (seen as running in a virtual machine on a server) is required to answer many questions: can we host it internally? In which hosting department? Are the capital allocators of this hosting department ok with this placement? How much does it save us and is it safe? Is there a better option in the Cloud? Etc. In this paper, we define the multi-objective VM reassignment problem for hybrid and decentralised data centres. We also propose H2¿D2, a solution that uses a multi-layer architecture and a metaheuristic algorithm to suggest reassignment solutions that are evaluated by the various hosting departments (according to their preferences). We compare H2¿D2 against state-of-the-art multi-objective algorithms and find that H2¿D2 outperforms them both in terms of quantity (approx 30% more than the second-best algorithm on average) and quality of solutions (19% better than the second-best on average).enThis is the author’s version of a work that was accepted for publication in Future Generation Computer Systems. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Future Generation Computer Systems, 2017-06. DOI: 10.1016/j.future.2017.06.015Large decentralised data centresHybrid cloudsVM reassignmentMulti-objective optimisationHybrid algorithmsInterval objectiveJournal Article79Part 275176410.1016/j.future.2017.06.0152017-09-12https://creativecommons.org/licenses/by-nc-nd/3.0/ie/