CompTIA Exam Prep - ITF+, A+, Network+, Security+, CySA+

A power distribution unit takes one high-capacity feed into a rack and splits it across outlets for the equipment inside. A managed PDU adds a network interface, so it can be monitored and controlled remotely. That one addition turns a power strip into an availability tool and, less obviously, into a device that needs securing. The four types Basic PDUs distribute power and nothing else. No network port, no display, no data. They are cheap and appropriate where power is monitored upstream at the panel. Metered PDUs measure current draw and report it, either on a local display or over the network. This is what lets you answer "how much headroom is left in this rack" before installing another server, instead of finding out when a breaker trips. Switched PDUs add remote control of individual outlets. You can power cycle one device without touching anything else, and you can define which outlets energize in what order when power returns after an outage. Switched and met...

MTBF and MTTF measure how reliable something is. They appear on Server+ under hardware planning and on Security+ under availability, and the pair is almost always tested together with MTTR. The three metrics MTBF — mean time between failures. The average operating time between failures of a repairable system. A server that can be fixed and returned to service has an MTBF. MTTF — mean time to failure. The average operating time until failure of a non-repairable item, one that is replaced rather than repaired. A hard drive or a power supply has an MTTF. MTTR — mean time to repair. The average time to restore a failed system to service. Note that in a security context MTTR more often means respond, repair or remediate depending on the stem — read carefully. The distinction that gets tested: repairable takes MTBF, replaceable takes MTTF . In practice vendors use MTBF loosely for components too, but on an exam the repairable/non-repairable split is the discriminator. How they fit...