When Does Powering Down Servers Make Sense? 301
snydeq writes "Powering down servers to conserve energy is a controversial practice that, if undertaken wisely, could greatly benefit IT in its quest to rein in energy costs in the datacenter. Though power cycling's long-term effects on server hardware may be mythical, its effects on IT and business operations are certainly real and often detrimental. Yet, development, staging, batch processing, failover — several server environments seem like prime candidates for routine power cycling to reduce datacenter energy consumption. Under what conditions and in what environments does powering down servers seem to make the most economic and operational sense, and what tips do folks have to offer to those considering making use of the practice?"
Re:Virtualize! Virtualize! Virtualize! (Score:5, Informative)
There are a number of tools and products out there to assist this.
Consider a large (65k+ employees) company that has a several hundred server implementation that they use to process payroll every two weeks. They use a management tool to power them up on Friday, process payroll over the weekend, and shut them down on Monday. The power and cooling cost impact of these several hundred servers *not* running most of the month (6 or so days a month instead of 31) is huge.
Another (and also in use by the same company) strategy is to virtualize the OS instances, spin those up and down as necessary, and then use something like VMWare's VMotion to maximize usage of the physical boxes - and again use another tool to power down unneeded compute capacity.
Welcome to the virtual world...
Lots of prerequisites, but when it works, it's pretty freakin' sweet...
Some criteria (Score:4, Informative)
1: Can your service be load balanced across several identical servers?
2: Does your services experience predictable but varying load?
3: Can the state used by your service be rapidly replicated (10 minutes) across newly booted systems?
Not all server systems make good candidates for shutdown. Web farms do tend to because they fit the criteria above.
PSU failures (Score:5, Informative)
The problem is the PSU, which fails most often during power-up. Leaving the servers always on has the advantage of avoiding that particular failure mode. Also, other components in the server are prone to failure during power-up, way more often than at steady state. So, powering up your computers is overall a risky moment.
VMWare can be used for this (Score:3, Informative)
VMWare has some cool functionality such that if you virtualize all your machines, at night time when the loads are lower, you can consolidate all your VMs onto a smaller number of physical machines, and automatically turn off the physical machines. Then, in the morning, as the loads increase, you can automatically power on the physical machines and move the VMs back onto these physical servers to handle the load. Not sure what it's called but when I heard about it, I thought it was really cool.
Re:Virtualize! Virtualize! Virtualize! (Score:5, Informative)
...and again use another tool to power down unneeded compute capacity.
And that other tool is ... VMware! DPM (distributed power management) is built right in, and does exactly what you describe.
http://www.vmware.com/products/vi/vc/drs.html [vmware.com] (scroll to the bottom)
Welcome to the virtual world...
Yup, the game is officially changed.
Re:Virtualize! Virtualize! Virtualize! (Score:5, Informative)
Actually, the other tool in this case is Cisco's VFrame Data Center. The problem with DPM (and other VMware tools) is that they won't let you move a physical box between ESX clusters. If you have multiple ESX clusters, the physical machine stays with it - powered up or not. With VFrame, the system can be powered down, removed from the cluster, and added to another if/when necessary... including any necessary network configuration (VLAN memberships, etc) and SAN configuration (zoning changes, LUN masking).
Not that I'm complaining about VMWare's solution to this problem - they're actually quite complimentary.
From someone who's been there... (Score:1, Informative)
We took our server estate down by a factor of 20 using modern virtualization hardware appliances and hypervisors [xen.org]. Thats right not 10x fewer servers, but 20x. With the right combination of investment in quality shared storage, dedicated virtualization appliances [360is.com], and the skills to make them work, today our cooling, power, and rack space bills arent worth worrying about.
We are rarely at the cutting edge of technology, but if we can do it, you can.
Re:Like a car... (Score:3, Informative)
Re:Virtualize! Virtualize! Virtualize! (Score:4, Informative)
And given that there's more to processing payroll than printing out a check for each employee (calculation of taxes in every state in the US, every country in the world, etc), updating various accounting systems, etc... there's a lot of work to be done besides "take 8 1/2 minutes for a single employee".
Re:Like a car... (Score:3, Informative)
Duplicate Server Shutdowns (Score:3, Informative)
I worked for a client that used a farm of web servers tied to their multiple Oracle systems. The web servers were all Sun Ultras balanced using Resonate as the balancing agent.
During prime time, we needed over 60 servers running but, between 6PM and 6AM, we only required about 15 to handle the load. By taking 75% off line every night (not always the same 75%) we reduced power consumption a great deal. By also shutting down 4 of the 6 Sun 6500s, we also reduced power of the data center.
In a year's time, we conserved over $80,000 in power alone and, had plenty of opportunity to perform off-hour upgrades and maintenance.
Failure rate due to power cycling was immeasurable.