Even when you have done all the right things, performed preventative maintenance, kept equipment at the right operating temperature, and used surge protectors, equipment will eventually cease to function. That is why many companies choose to maintain service-level agreements (SLAs). An SLA is a contract with a hardware vendor that provides a certain level of protection. For a fee, the vendor agrees to repair or replace the equipment within the contracted time.
You'll also need to know two important numbers when purchasing equipment or attempting to calculate how long the equipment will last. First is the mean time between failure (MTBF), used to calculate the expected lifetime of a device. The higher the MTBF is, the better. The second number you'll need to know is the mean time to repair (MTTR). The MTTR is an estimate of how long it would take to repair the equipment and get it back into use. For MTTR, lower numbers are better.