220-1101 Question 306
Single answerRedundant power supplyA technician is replacing a failed power supply module in a rack-mounted file server used by a small medical office. The server remained online when one module failed, and the office manager says there was no interruption to users. The technician wants to explain why the server stayed operational and what requirement must still be met for this design to provide the intended protection. Which of the following is the BEST answer?
- A
The server uses a redundant power supply, and each power module should be connected to separate power sources or circuits when possible.
- B
The server uses a higher-wattage single power supply, which can continue operating after an internal PSU failure if the load is low enough.
- C
The server uses a UPS, which automatically replaces a failed internal server power supply until the failed PSU is swapped.
- D
The server uses PoE, which allows network switches to keep the server powered if one internal power supply fails.
Show answer and explanation
Correct answer: A
Explanation
This scenario describes a classic redundant power supply setup commonly found in servers. In A+ Core 1, candidates should recognize that redundant PSUs improve availability by allowing a system to remain operational if one PSU module fails. Many server PSUs are hot-swappable, letting a technician replace a failed module without shutting down the server. However, redundancy is most effective only when each PSU is connected to independent upstream power paths, such as separate wall circuits, PDUs, or UPS units. If both PSU modules are plugged into the same power strip or same failed circuit, the system still has a single point of failure. This aligns with standard server hardware best practices documented by major vendors such as Dell, HPE, and Lenovo in their server deployment and power redundancy guidance.
- A. Correct.
Correct. A redundant power supply system uses multiple hot-swappable PSU modules so the server can keep running if one module fails. For the redundancy to provide meaningful protection against power loss, best practice is to connect the separate PSU modules to different power sources, PDUs, or circuits when available. Otherwise, a single upstream power issue could still take the server offline.
- B. Incorrect.
Incorrect. A single higher-wattage PSU does not provide redundancy. If that one unit fails, the server loses power regardless of its wattage rating. This option reflects the misconception that capacity and redundancy are the same thing.
- C. Incorrect.
Incorrect. A UPS can protect against building power fluctuations or outages, but it does not replace a failed internal server PSU. If a server has only one internal PSU and that PSU fails, the UPS cannot power the motherboard directly through the failed unit.
- D. Incorrect.
Incorrect. Power over Ethernet is used to deliver low-voltage power to devices such as IP phones, wireless access points, and some cameras. Standard servers are not powered by PoE, and PoE does not serve as a backup for failed internal server power supplies.