"The reality for most enterprises is they don’t write their apps, they have many apps for many workloads that require different servers and solutions.There is undoubtedly going to be a level of inefficiency built into the system," he said.
For example, some companies deliberately build in excess capacity and have systems standing by to take over when greater load capacity than usual is required. So they might overprovision for peaks and demand.
Then there's Shadow IT, the people who go into business for themselves within a company and skirt official company policy on IT. Some departments don’t utilize official enterprise channels and buy their own machines. And then there's merger and acquisition activity, where redundant systems might be set aside but not actually shut down.
John Abbott, director of advanced technical services at Centrilogic, a cloud services provider that also does migrations, runs into this all the time, especially now that he's doing Windows Server 2003 migrations. He said about 75% of his customers have at least some servers not being used, and that the larger the data center, the more likely there are things running no one knows about.
"What we find with these discoveries is where a server was set up and the app owner changed their mind or the app never got approval or they are proof of concept servers that never do anything," he said.
In his experience, zombie servers tend to be older most often because the person(s) using it have moved on one way or another and the server was never repurposed or decommissioned.
"Over time, what you find is the people with the knowledge of the environment change jobs or get let go and there is no knowledge transfer. No one knows what those servers are so they don't touch them. They assume if it's there it's running in production and they don't do anything with it," he said.
One of the biggest sources of help in flushing out zombie servers has been the Windows Server 2003 end of life this past July and subsequent migrations by firms off the aged operating system. Most firms used the end of support for Server 2003 as an opportunity to take a full and complete inventory of what they have and that is rooting out the zombies.
"The Windows Server 2003 project is straightening a lot of this out because people are analyzing their current inventory so that at the end of this they have a compete inventory," said Abbott. "Server 2003 helped expose this because otherwise no one would look at them. If they aren’t broken people aren't going to address them."
How to prevent the problem
Sign up for CIO Asia eNewsletters.