"Sprawl is the typical problem there for companies that are not doing lifecycle management or automating any of the procedures involved in systems administration or support," Staten says. "That's where the change in thinking needs to happen or progress typically starts to slow down." At the most basic level, it's necessary to know what all those virtual machines are doing, or whether they're doing anything at all.

Data-center administrators consistently report that about 15 percent of the servers they maintain aren't doing anything useful. That is, they're running and being properly maintained, but are not being used by any end users or applications in an average month, according to Sumir Karayi, CEO of 1E software, a U.K.-based asset-management vendor that sponsors regular studies of resource-utilization efficiency in data centers.

"IT is typically asked only for uptime; their job is to keep things running, not ask why it's running, so they look at utilization of resources, not workloads." Karayi says. "If a server is being backed up, patched, rebooted to install patches, it can look quite busy just doing housekeeping work even when no one is using them. With virtual servers it's even easier because there's not as much of a perceived cost to running them without doing any real work."

Restricting sprawl doesn't keep most companies moving on ambitious migrations, Wolf says.