The 800FMR power supply is a redundant front mount unit. Three power modules are used to create a power supply that will continue to provide power even if one of the module fails. This provides a huge amount of reliability and uptime for the server, making redundant power a staple of mission-critical servers. The power modules are hot-swappable so they can be changed without turning the server off.
The 800FMR is identical to the 600FMR in every way except that it has a higher power output making it a better choice for our 25X system or servers with many hard drives.