Powering Down Servers Is a Calculated Risk
Given the high costs of electricity, datacenter operators are feeling increased pressure to rein in energy consumption. Server virtualization and consolidation are proving effective, but another straightforward approach to energy cost-cutting seems to be met with reluctance: the practice of powering down servers that aren't in use.
In a recent InfoWorld article, InfoWorld Contributing Analyst Logan Harbaugh proposed that powering down servers during off-hours would cut energy waste while not having any adverse effect on the hardware. He even suggested that companies could use the waiting time required to power up servers as a bragging point to users: "This is taking some time because we're being energy conscious and environmentally friendly."
Harbaugh's article met with resistance from a number of readers. In some quarters, shutting down servers is tantamount to heresy. Several readers protested that pulling servers offline is simply bad customer service; in their shops, servers never stop. Others were concerned that powering down a server could be harmful to the machinery. I thought it would be prudent to go directly to some of the vendors and ask them about the practice of shutting down servers that aren't being used.
I discovered that even the experts don't quite see eye to eye on the issue. Ken Baker, datacenter infrastructure technologist at HP, said powering down servers is completely safe. "It's not at all bad for the server. It's something we do to electronic devices all the time. It can handle it from a hardware perspective," said Baker.
But Brad McCredie, an IBM fellow for the Systems and Technology Group, wasn't quite so sanguine. He explained that, technically speaking, powering off and on any kind of computer can have a detrimental effect over time.
"[Temperature cycling] is a well-established failure mechanism and a stress on components," McCredie pointed out. "What it really comes down to is all these things -- chips soldered on modules, soldered on boards and connectors -- that expand and contract when they heat and cool.... When they all contract and expand at different rates, they can fail. That's ultimately the bad thing with power cycling," he said.
Mark Monroe, director of sustainable computing at Sun, suggested that machines can handle being shut down a finite number of times. Arguably, the number is large enough for regular power cycling over an extended period of time. "Most server vendors today say they'll support a certain number of cycles of powering things on and off," Monroe said. "I believe most of the server vendors would say [the number] is in the hundreds as opposed to the thousands."
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.