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(in the office) Today, the UPS battery replace warning light lit up and there was a slight panic as the all the technical people will not be around the next few days.

But after thinking a bit further, I realise that in case of power failure, no client computers will be able to turn on in the first place and operations will be disrupted regardless of whether the UPS keeps the server up.

This makes me wonder if the UPS is really such a critical component? What do you think?

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Think of if this way, that instead of stopping your car, then putting it in park, then turning off the key, you throw it into park while moving and let the engine shut off by itself. – DanBig Jan 7 '11 at 15:40
Thanks everyone for the responses. Yea, I think you guys are right that the UPS is good only as far as allowing for graceful shutdown and prevent data corruption. I picked Michael's answer because he directly provide the solution to address my concern of business disruption. Thanks all again =) – Jake Jan 8 '11 at 15:24
up vote 5 down vote accepted

A UPS is for allowing graceful shutdown and avoiding a shutdown during a short outage, not maintaining availability during an outage. For maintaining availability the only real solution is a backup generator that kicks in whenever a monitor detects that the power's been out for more than five minutes or so.

This also means that a UPS is pretty useless on a server without a daemon set up to respond to critical events: apcupsd is the usual one on a linux server.

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One thing to consider is that if a server loses power unexpectedly, it may experience data corruption. A UPS gives the server time to shut down in an orderly fashion.

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Yes they are. In your situation, they're less about making sure resources are available to clients during a power outage and more about providing power to the servers to allow them to be gracefully shut down during a power outage.

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Guess that all depends on your SLA's and what business you're in. I work in a Tier IV datacenter. We use batteries, but only to facilitate the transition to generators. We are much less concerned with users inside the company being able to work, than we are of our clients being able to access our systems.

Users don't pay us, but clients do. And if the systems aren't available to them, we aren't making money. But again, it all depends on your business.

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Unfortunately, my answer to this is that it depends on the role of that server. My biggest concern w/losing power to any device is corruption. I refuse to allow even one of our servers - production or development - to be in a position where there is a SPOF as far as power is concerned.

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At our location, the client computers (and networking equipment in between) are ALL on UPS. So people can safely close down their local and network resources during power failures. Having the UPS on the server is important to help avoid data corruption there, but if the client was in the middle of updating something, you can still end up with data corruption. It's important that the entire chain is protected as much as possible. If you can only pick one location though, I'd pick server...

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As many of the responses are pointing out, UPS is not a be-all-end-all solution.

It's part of a comprehensive approach to keep the electrons flowing to critical systems if there's a disruption.

This allows for either enough time for a graceful shutdown rather than a hard crash or it possibly smooths the transition from one power source to another (generator or another power feed).

I'd be concerned if any system I was responsible for wasn't on UPS if I couldn't afford to lose the data or be down waiting for a restore or system rebuild.

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