CACM: Current-aware capacity management in consolidated server enclosures

Using virtualization to consolidate servers is a routine method for reducing power consumption in data centers. Current practice, however, assumes homogeneous servers that operate in a homogeneous physical environment. Experimental evidence collected in our mid-size, fully instrumented data center challenges those assumptions, by finding that chassis construction can significantly influence cooling power usage. In particular, the multiple power domains in a single chassis can have different levels of power efficiency, and further, power consumption is affected by the differences in electrical current levels across these two domains. This paper describes experiments designed to validate these facts, followed by a proposed current-aware capacity management system (CACM) that controls resource allocation across power domains by periodically migrating virtual machines among servers. The method not only fully accounts for the influence of current difference between the two domains, but also enforces power caps and safety levels for node temperature levels. Comparisons with industry-standard techniques that are not aware of physical constraints show that current-awareness can improve performance as well as power consumption, with about 16% in energy savings. Such savings indicate the utility of adding physical awareness to the ways in which IT systems are managed.