Both Monroe and McCredie note that their respective companies already offer software capable of powering down components of a server, in the interest of boosting energy efficiency. "We just released a new product that has the capability of turning different parts of the server off: disk, CPUs, fan [and] memory DIMMS will be powered down," said Monroe.
Similarly, IBM offers a product called Active Energy Manager, an extension to IBM Systems Director, that features advanced energy control options designed to boost performance per watt by slowing processor clock speed or even putting processors in "nap" mode when not in use.
Beyond the hardware concerns associated with powering down servers, there can be headaches associated with powering on a server from an operational perspective, according to Sun's Monroe. "There are concerns about changes being made to a server config file but it not being recorded in the log. It will take effect at the next reboot, and lo and behold, the system won't come back up," he said.
HP's Baker shared similar sentiments about the difficulty of getting a server back to an operational state after it's turned back on, which is why powering down might be disconcerting for some organizations. "In an enterprise operating system, or depending on the application you're running, it may not be appropriate for it to be controlled in that manner," he said. "Can you automate that process? Certainly. There's a lot to some of these applications, though, in terms of complexity. Can you automate the functionality that allows the server to be turned back on, log in, load all the necessary software ... and get it on the network to do some work? It's certainly possible. It could be a time-consuming process."
Some companies say they're already powering down servers that aren't in use. One company that strongly advocates the practice is Cassatt. The company offers a software solution, called Cassatt Active Response, that automatically powers servers off and on in response to preset conditions, whether time-based (e.g., powering down servers at the end of the workday and on weekends) or related to application availability (if service levels for a given app reach a certain threshold, a new server would fire up).
Notably, VMware offers "experimental" functionality in VMware Infrastructure 3.5 for powering off and on servers called Distributed Power Management. It's designed to automatically power off servers not currently needed in order to meet service levels, and automatically power on servers as demand for compute resources increases.