Answer by David Chapman
How important is it that your data integrity is maintained and that your users have instant access to it?
A (static) UPS has a finite energy store so that, in the event of a supply failure it will provide power for a short time. This available time can be used in several ways depending on the needs of the organisation.
It can be used (and most frequently is used) to perform an orderly shut down of the network and servers. This protects transactions and ensures integrity of the data. However, once triggered, the process allows no new access to data - i.e., your users have no service. Service is only restored after the power supply has been re-established and the servers and network devices re-booted. If the operation is losing money by the minute, this is unlikely to be acceptable!
Another approach is to use the limited time available to start up an auxiliary generator to take over the supply from the UPS. This allows the operation to continue as if nothing had happened - assuming of course that the generator and fuel supply are properly maintained and work as expected.
Alternatively the time can be used to transfer transactions to another site, either an active peer site or a passive standby site. Again, as far as users are concerned, nothing has changed.
Whatever approach is taken it is most important that the standby power available is used carefully. Only essential equipment should be connected to the UPS system - servers, communications, network devices, essential PCs - no coffee machines, laser printers, etc.!