UPS vs Duplicating

Most Servers and high end Network devices have 2 Power inputs ,But Many other devices like basic switches as an example have only one, So even if the Server is Up and running in case of shortage , if there is a problem with the switch...  , the switch will go down because it is on a differrent circuit ... So nothing would work .

How can i Set up power redundancy for those with one power input ? Better of using Separate UPS ? Or Buying the same network equipment ?

Whats are the pros & cons ?...And anything else i should know regarding it ? Any other way of doing it ?

Thank you
Maidine FouadEngineerAsked:
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The 2nd powersupply on servers is for redundancy, should one of them fail, the other takes over and the server keeps on running so you don't have data loss. That doesn't mean you shouldn't also have a UPS. The UPS is there for power outages, and if there is a power outage, the UPS sends a shutdown signal to the servers so they are gracefully shutdown while the power outage lasts. That way you don't loose data. A UPS isn't meant for users to keep on working during power failures, it is meant to give the servers enough grace period for them to shut down gracefully.

The switches don't really matter. If they go down, the users might not be able to access the servers, until you have replaced the switch, but the data on the servers would still be safe.
Just adding to Rindi's excellent comments......

A UPS on the switch will allow users to continue functioning, but only if the users' computers have some sort of battery backup also.  Of course, this assumes that power goes out to everyone.

An important key here is to educate users to shut things down as soon as power goes out.  You can't be sure how long the UPSs will operate.
JohnBusiness Consultant (Owner)Commented:
I like to keep network gear on a separate UPS so that the network stays up in the event of a power failure. This is in addition to servers. We have occasion to let one of us in in the event of a failure and a decent UPS will keep the network (basic network) going for a while - probably longer than the servers.
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Any single component of your environment is liable to failure; you maintain high availability by having redundancy. Of course, some components have a greater likelihood of failure than others, so you need to pick your risks.

If you have dual power supplies in your servers, you probably want two separate UPSes to feed them.

What I've seen done with switches (which I almost never see with dual power supplies), is stacked switches, powered from different power buses or UPSes. You have to design your network connectivity so each server has a path through two or more switches. In virtualization situations, you want to have the same duality for the shared storage and the paths between it and the servers.

At some level, though, you just give up on spending a lot on extreme single-site redundancy and figure out how to carry out your business with two independent sites that can cover for each other if one should experience a failure, across the whole spectrum of possible failures.
Don JohnstonInstructorCommented:
The switches don't really matter.
I'm guessing you're not in a data center. :-)

Switches have redundant power supplies as well. Just about all the Cisco enterprise switches have redundant power supply capability.
Danny ChildIT ManagerCommented:
I view the main purpose of the UPS as being the voltage *smoothing*, rather than maintaining the supply.  So, it can cope with spikes, surges, brown-outs, etc.  Guess this depends where you are in the world, really...

In 10 years in my current role, we've only had one full power cut, but probably get a spike every 6 months or so.  

PSUs inside servers are have to work pretty hard, with cooling fans etc, and are quite prone to failure themselves.  Hence having multiples is a good idea.  
Switches tend to be more robust overall, with no moving parts (barring multiple, resilient, fans) so I'd say they were less vulnerable.
Of course, if you pull the plug out by accident, there's not much you can do about that.  However, decent Cisco kit even has velcro ties on the rear to stop that happening.  Or, you have them stacked, as above.  And of course, the switch should be fine when powered up again - whereas a server may well be VERY unhappy about a full dirty power-down.

If you're worried about a Power Cut AND a failed UPS, and needing a second UPS to power things, I'd say that's a pretty remote chance of occurring.g

The point above about your users needing their OWN UPS's in order to use your network is very valid too.  We bought a £30,000 APC UPS for one of our sites, and it runs our Comms Room, all floor-level network racks, the entire VOIP phone system, and PCs for 6 of our staff - which is about 10% of the staff at that location.  It claims a run-time of 2.5 hours, which is enough to get their critical work done, perform some controlled shutdowns, and start the move to our DR site.  

The next level above this would be generators, which are awkward to site, and you have problems about exhaust locations and fuel storage, which can be tricky in a congested urban environment, where this building is.  You still need the UPS to do the smoothing, and to give power while the generator spins up to speed.

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JohnBusiness Consultant (Owner)Commented:
I do not need voltage smoothing where I live - power is very reliable, surge and spike-free and works in a very narrow band of voltage.  So when it does go out for more than a minute or so, it is usually out for long enough to make me happy I have a good UPS in the basement.
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