I wounder how important it is to have an UPS for a server. Everyone seems to use UPS for servers but not for client computers.
In example, if I use Windows Small Business Server on a small network for Active Directory and storing the users home directory for backup is it still useful with an UPS, why? If a power outage happens, shouldn't the filesystem handle that, so no files are corrupted? And in this case I think the problem is the same on the clients.
I do understand that it can be useful on servers when changing the server configuration, but that is done during a very limited time and it sounds like it's more worth to do good backups before the configuration.
And when thinking about database transactions, I think that the transaction logic in the database management system should handle it, that's what transactions are for.
And finally, if an UPS is used, doesn't the server applications need to have support for it? outherwise the power outage is only delayed? Or is it only the operating system that needs the UPS?
The brief interruption to someone's work is more likely going to cost less than buying and maintaining a desktop UPS. That's one of many reasons why many professional solutions are server based and centralized, as the service level can be focused there.
If there is a business justification with Return On Investment (ROI) in your environment, I would suggest a cost analysis between providing generated or battery backed power to the entire building versus buying individual UPSes for every workstation.
A server does not necessarily need to "support" a UPS, it's just a battery that's inline with the power source. Any "support" is going to be automatic shutdown or taking a preferred action in case of power loss.
The idea is to protect the equipment by conditioning the power as well as allowing the equipment to be properly shutdown in case of an extended outage. Depending on your budget, it is also often to maintain availability in case of power loss but with that service level you often have power generation in addition to a UPS.
A UPS is in addition to backups and has no direct correlation to backups beyond being a best practice within properly run IT infrastructure.
Without a UPS you could lose data, have hardware failure, and have system availability interrupted. It is often easier to find the ROI here than with workstations.
Accidents do still happen. RAID cache batteries not working properly is a concrete example, but journaling filesystems and transactional integrity simply aren't guaranteed when the power is pulled.
Plus, any UPS worth a damn also does line conditioning to protect the hardware from current and voltage variations, extending the lifetime of your hardware.
Why servers and not desktops? Some places do, but it's expensive. How much is the data on any client worth? How much is the data on the server worth?
There are many, many reasons to use a UPS, but using your example of DB transactions, look at it this way. Even if a transaction is committed, you lose power, and your RAID write cache (you are using battery-backed write cache, correct?) batteries aren't functioning properly, you're out of luck.
Additionally, power outages are notoriously hard on equipment. Replacing a $500 workstation is one thing, but it's much more painful (both financially and otherwise) to replace a server that costs an order of magnitude more (data on that server notwithstanding). Most good UPSes also are line-interactive and will offer much better protection from power surges and brownouts than you'd get with a cheap power strip.
Overall, it's just a very well-accepted best practice.
What does using a UPS have to do with changing a server's configuration?
Who says that clients don't need a UPS? All systems in our environment are protected by a UPS - from every server to each desktop.
You are correct that a UPS only delays the power outage. However when a power loss occurs the UPS communicates to the OS through a USB cable (most common nowadays). This allows the UPS to notify the OS when the battery is about be empty and the OS can begin gracefull system shutdown. This is something that is not possible in a normal power outage without a UPS. The power company will not call you and tell you that a tree is going to fall in 10 minutes and kill your power.
Your assumptions about how a computer handles a loss of power are not realistic. Most of the time there might not be any harm, but there is no need to gamble. One problem on a production server and you will rue the day that you decieded you did not need a UPS.
Jonas,
It's a wonderful thing to THINK the OS should handle an outage - and it SHOULD. BUT, reality differs. Reads and writes take place very quickly but if it loses power at the wrong moment, you lose the information.
Do you want your server rebooting because the lights flicker? Some servers can take 10-15 minutes to start up and then have to go through a disk check when they aren't protected. Users accessing the server via laptop and the internet won't necessarily experience a problem, but you could end up WASTING your employee's time or worse - if an employee is in the middle of a proposal and hasn't saved the file, you could lose business. UPSs are not very expensive in the grand scheme of IT costs and should be used in ANY place that is subject to even occasional outages. If you think the $100-300 isn't worth it for the server and $50 isn't worth it for the PC, that's your prerogative. But most people understand TIME is MONEY and any disruption in work flow will cost you money.