Formal Problem Settings Sample Clauses

Formal Problem Settings. = We consider a single host H with processing power M that can run at variable speed hj(j = ≤ ∀ ∈ 1, 2, ... , L). Note that these levels are discrete. Virtual machines are represented by Vi (i 1, 2, ... , N) . Each Vi has a maximum processing requirement of Mi , which can change with the time but cannot exceed M, i.e., sup Mi M i [1, N]. Current processor requirement of Vi at time t is represented by Cit. Cost of SLAV per unit time is Cv. Vs represents the start time of SLAV and Vf is the time when SLAV ends, i.e., the processing requirement of the current host decreases again after SLAV. Migration time for Vi at time t is a function of Cit and is modelled as f (Cit). Migration cost per unit time of Vi starting at time t is modelled as g(Vit). m is the time point when migration is initiated by an algorithm. Total cost includes migration cost and SLAV cost. ∈ Without loss of generality, we assume that at each time point t [1, T], either a new virtual machine Vi with a processing requirement Cit arrives or an existing virtual machine modifies its processing requirement. The host H is oversubscribed if the sum of all processing requirements at time of virtual machines assigned to host H at t i=1 t is more than the processing power M of the host, i.e., K C > M, where K ≤ Nis the total number . When the host is oversubscribed, Service Level Agreement Violation (SLAV) occurs, i.e., the host is unable to meet the processing demands of the existing virtual machines. At this stage, the algorithm has two choices. One, to provide an inferior level of quality of service and continue accruing SLAV cost. Two, to initiate a virtual machine migration by transferring a virtual machine to a new host and incur a migration cost. The decision has to be taken without the knowledge of future virtual machine arrivals and change in the processing requirements of the existing virtual machines. The research problem is to design an optimal algorithm that can decide if virtual machine migration shall be initiated when a host H is oversubscribed (resulting in extra energy cost of the new physical host), or to delay the instantiation of the new host and accrue SLAV cost.