What do I mean by zombies in your datacenter? Zombies are the living dead servers, both virtual and physical, that you have in your computer room. These servers are no longer in production, however they have not been decommissioned or removed.
In the case of physical servers they are occupying rack space, may be consuming power, and generating heat that must be removed from the data center. In addition, network connections and storage capacity, allocated to these now deceased applications, have become unused resources.
In the case of virtual servers you might argue that they are not consuming resources, however, they are occupying albeit a minimal amount of processor power and storage and/or network connections might be allocated to these virtual servers. Thus other resources are negatively impacted by the existence of the zombies.
From the financial perspective what we have here is money being spent for no reason at all. Our electric bill is inflated because of the zombies consuming power and air-conditioning resources, thus negatively impacting operating expenses. Since the zombies are consuming datacenter assets, we lose the opportunity costs of the network connections and storage capacity. We may perhaps even by additional switch connections and/or storage under the impression that insufficient assets are in place because of the zombies consuming these scarce resources. Thus capital expenses are negatively impacted by the zombies.
Housecleaning may not be a high priority action item in the datacenter. Over the years the zombies increase in numbers and we become more and more inefficient, and the funds to maintain them continue to grow. Recent studies indicate that only 35% of our processing power in the datacenter is actually in productive use, yet we continue to pay the operating expenses for the remaining 65%. Given the magnitude of our zombie problem the time has come to purge the datacenter of these monsters and reduce our costs.