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When Does Powering Down Servers Make Sense?
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?"
Like when someone posts your domain name on slashdot!
You can't take down a server that's already off-line.
you see the Windows logo appear? (sorry, couldn't resist)
Attention all planets of the Solar Federation! We have assumed control! - Neil Peart
The best time to shut down the servers is right before you quit your job. Password-protecting the BIOS first adds value too.
Put redundant/failover servers into a sleep state and enable WOL.
It's pretty much up to your business....what must run 24/7, what systems are likely to get accessed in off hours, and how likely is that, and how critical are they? With redundant systems, can there be any downtime while they are powered up, or should it be immediate failover? If you use virtualization the redundancy should be easier to manage in many cases...you may be able to immediately offload to running systems and power up backup systems and then bring the VMs up there.
It's hard to get very specific without knowing your business and what you are running and what the needs are.
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I'm glad this was posted to "Ask Slashdot" where your audience is highly seasoned professionals that can give you wise, insightful answers...
In the data center that I manage, I use a few simple rules to determine when I power them down.
1) If the server is on fire
2) If there are no users using the server
or
3) If the power company is saying that I haven't paid my bill and they are sending "Hank" over to cut me off
4) Civil unrest, tornado, earthquake, zombies, etc.
If you virtualized your servers, you could create a managed power-down/power-up scenario. In the morning, your servers would turn on, your virtualized instances would move around (so they have more power for the day's activities), and then at night they'd retreat to a smaller group of servers. The unused servers could shut down for the night. You could even rotate which servers stay on overnight keeping the virtual servers running to spread the wear around if there is some.
Seriously, this analogy makes sense. When a car is cruising on the high way it's able to maintain speed using 4/8 cylinders. Servers could be cycled in a similar fashion. Do you really need 20 web servers running at 3 am on a Sunday?
When you're sure you don't need it to come back up.
You don't make the poor richer by making the rich poorer. - Winston Churchill
How many of us have servers that don't need to be live? Yeah, I guess there might be a development server, but that assumes that you're not developing. There could be a failover server that does nothing when the primary hasn't failed, but in that case you'd want to be damn sure that the failover will come online without difficulty when it needs to.
It seems to me like it would be a pretty rare case when this is applicable. I'd sooner be interested in asking, can they build servers that can selectively power down subsystems that aren't currently in use, sufficiently enough that there's no serious harm. For example, I'd consider putting some of my fileservers' hard drives to sleep over night, but I'd still want the server to be available and the drives to spin back up if I log in from home and need access.
Mostly, I'd say that if you have servers that you don't need to be live, you might not be using your servers efficiently. It may be worth looking into setting up some kind of VM server with various images that can be brought up on command. But hey, if you do have a server that you can turn off without causing problems, go for it.
Powering down your servers tends to introduce response issues. :-)
Some servers, like the HP ProLiant line, has power management features. Try experimenting with features like these first.
What kind of UPS does that? If the batteries are already charged, what would it be doing with the power that's not consumed by the devices - does it also act as a space-heater?
The ratings for UPS's - and any other power supply - are peak loads, if the UPS is being used at 100% capacity.
Full disclosure, I work for Citrix. Check out XenServer, which can remotely provision server workloads to virtual and bare metal machines - based on load, you can remotely power up resources as needed. I have seen the future, and it is awesome. And green.
Atari, System V, C64, Amiga, College Unix (?, I wasn't like root or nothin'), Mac, WinNinetySighs, NT, Novell, Win2K, So
My guess is that managing energy consumption by powering down servers is the wrong way round - there seems to be a fair bit of interest in developing hardware that manages it's own energy consumption without loss, either in additional power to bring it back up to speed or in processing lag, etc. Of course, this doesn't address the poster's immediate concerns to which I have little to add other than it's probably good to cost in heightened risks of hardware failure and therefore the costs of unscheduled downtime.
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.
Deleted
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.
"The agriculture ministry is not in charge of Gundam" - Japanese ministry official.
As long as power use is built into the fixed price I pay for the cabinet I rent at the colo, I'll never turn off my servers if I don't need to. Why would I?
Analogy (this time, light bulbs).
- Light bulbs fail just as you turn them on. Or off.
- They hardly ever fail whilst switched on.
I think servers are the same. You're in trouble if a server you've had switched on for two years and forgotten about loses power and doesn't come back up. If it'd been switched off every weekend it would have failed earlier -- but probably at a more convenient time.
(My datacenter charges about a buck a VA)
A watt?
chris@xanadu:~$ whatis /.
/.: nothing appropriate.
Power outages present a very different scenario to the system from powering things down the right way...
On second thought, let's not go to the internet. 'Tis a silly place.
I would think that if any servers can be regularly powered off, then they probably fall into one of two categories, they aren't really needed or they are only loaded at certain times. In both cases there's a good reason for consolidation, whether it be physical or virtual. obviously virtual gives the best bang for buck. I run several ESX clusters and despite dept's not trusting virtual servers, they all come around in the end. I think virtuals really are the only way to go to really save money, space, power, and the all important UPS load. Don't forget, the myth about hard disks dying after they have been running for a long time and then allowed to cool after a power failure, well that myth isn't a myth, it happens, and it happens a lot.
I cannot think of situation where powering off a server that is needed provides any benefit whatsoever, you might save a few dollars, but as we all know when you're IT dept struggles to get budget for anything, the risk of failure and the HUGE costs associated with that far outweigh ANY power savings you might achieve.
I don't give a rat's arse if powering off a few minor servers saves $100 a month, when if the disk dies after it cools down, and I then have to go into repair mode to find out what peculiar apps were installed on the server, somehow scrounge another system with no budget, and then rebuild the whole damn thing, only to find out the developers have changed so many configurations it takes weeks or months before everything is really working as it should. Even more joy is that usually occurs at night if power is lost, as we have nothing better to do anyway. NO THANKS!
For companies who have massive budgets for IT, and routinely swap out hard disks, etc, maybe that would work, most companies I know and have worked for over the years though tend to view IT as a parasitic loss centre run by people who spend there days watching the blinkety lights and having fun, "it's just a bunch of servers, how hard could it be" or "how much money could they need, I can go the PC shop and get a whole quad core rig for $600!"
But I will say, nothing gets Capital Exp forms signed faster than a major downtime!
... is with electronic voting servers, to force paper ballots and more accurate counting.
I personally think a buck for a Virginia would be a great deal.
On a side note, that seems pretty pricey for a watt - turning on my blow dryer in the morning would cost me $1500 where you live. I'd have to go to work with wet hair everyday.
Ooooh - I could instead use solar energy to dry my hair (stand outside in the sun for a while). Green is good!
Light bulbs fail when they're turned on because there's a warmup spike as the electricity flows through the wire. This causes the tungsten to heat up more than it will when the circuit is complete, and break the circuit.
If your lightbulb fails it's because the filament has worn down - it's just that you usually find out about it when you turn the light bulb on or off.
Also, your analogy means nothing. Servers are nothing like light bulbs.