Your NAS is probably one of the most expensive pieces of equipment you own, and it’s storing hundreds of gigabytes of memories and valuable files.
So why is it not hooked up to a UPS? Let me tell you why not having one is a horrible idea.
The obvious one: it protects you from power outages
Credit:Â Patrick Campanale / How-To Geek
The main reason why you should get one is the same one you were thinking when you opened this article: power outages. This is the most dramatic and visible threat to data integrity, yet many underestimate exactly what occurs mechanically and digitally during a sudden loss of electricity. Keep in mind that a NAS is not simply a hard drive enclosure; it is a complex server running a specialized OS that constantly manages file tables, journals, and cached data in the system’s random access memory. When you initiate a standard shutdown, the operating system meticulously stops running processes, flushes data from the volatile RAM to the non-volatile storage, and signals the mechanical drive heads to park safely.
Without a UPS, the immediate loss of energy prevents the read/write heads of the hard disk drives from parking correctly, which can lead to physical platter damage in older drives or significant wear in modern ones. More critically, any data that was temporarily held in the write cache—data that the system “said” was written but hadn’t actually hit the magnetic platter yet—is instantly vaporized. Completely gone. That’s how temporary storage works. This discrepancy often leads to file system corruption, where the directory structure of the drive no longer matches the actual data stored, resulting in “orphan files” or completely unreadable volumes.
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A UPS fixes this. I’m not saying it has to necessarily to keep the server running for hours during a blackout, but it will provide a window of time—usually just a few minutes—for the NAS to detect the power failure via a USB data cable. Once detected, the UPS software triggers an automated, graceful shutdown sequence. This ensures that all caches are flushed to the disk, the file system is consistently unmounted, and the hardware powers off exactly as the manufacturer intended, preserving the physical health of the drives and the logical integrity of the data they hold.
It protects your NAS from dirty power
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A complete blackout is a binary event—power is either on or off—but your electrical grid also subjects sensitive electronics to a spectrum of irregularities known collectively as “dirty power.” Wall outlets rarely deliver a perfect, steady 120 or 230 volts. Instead, the supply is often plagued by voltage sags, brownouts, frequency noise, and high-voltage spikes. A NAS is filled with delicate microprocessors, RAM modules, and disk controllers that rely on stable voltage to operate at specific frequencies. And when the input voltage fluctuates significantly, the internal power supply unit (PSU) of the NAS must work overtime to rectify the current, leading to increased heat generation and premature component failure.
Brownouts are particularly insidious for storage devices. When voltage drops below standard levels, electronic components often try to draw more current (amperage) to compensate and maintain the same power output. This surge in amperage creates excess heat and electrical stress that can slowly degrade the motherboard and hard drive logic boards over time. A standard surge protector offers no defense against this; it only clips the top off of high-voltage spikes but does nothing to boost low voltage.
A decent line-interactive UPS helps mitigate this issue through a feature called Automatic Voltage Regulation (AVR). AVR allows the UPS to monitor the incoming voltage continuously. If the voltage dips too low (a sag) or jumps too high (a swell) without actually cutting out, the UPS uses an internal transformer to boost or trim the voltage back to safe levels without switching to battery power. This ensures that the NAS receives a clean, consistent sine wave (or simulated sine wave) of power. Thus, extending its lifespan. Pretty cool.
It protects you from write holes
Credit:Â Patrick Campanale / How-To Geek
If you don’t know what a “write hole” is, it’s a specific and dangerous failure mode associated with RAID configurations, particularly those that use parity, such as RAID 5 or RAID 6. These RAID levels work by stripping data across multiple drives and calculating a mathematical checksum, or parity block, which allows the array to rebuild data if a drive fails.
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For every piece of data written, the system must write the data itself and then update the corresponding parity information. These two actions are intended to happen simultaneously, but in reality, they are sequential operations that occur essentially back-to-back. If a power failure occurs at the precise millisecond between writing the new data and updating the parity block, the array enters a state of inconsistency. The data on the disk strips no longer matches the mathematical parity meant to protect it—hence, resulting in a write hole.
The worst part, though, is that the RAID controller may not immediately realize the error. The stripe looks valid until you attempt to read that specific block or try to rebuild the array after a drive failure. At that moment, the controller relies on the parity to reconstruct missing data, but because the parity information is “dirty” or outdated from the unfinished write, the reconstruction will fail or produce corrupted gibberish.
Using a UPS is the most effective hardware-level defense against the write hole phenomenon for consumer and small business NAS units that lack expensive battery-backed write cache controllers. As we told you, it ensures a continuous stream of power to your NAS, including during the write operation, thus ensuring that the transaction—writing both the data and the parity—always completes successfully. Even if the lights go out in the building, the UPS keeps the voltage flowing long enough for the RAID controller to finish the stripe update, ensuring that the mathematical integrity of your array remains absolute and preventing silent data corruption that might not be discovered until it is too late.
It avoids RAID sync failures
Credit:Â Patrick Campanale / How-To Geek
Finally, but not least importantly, it helps with another RAID issue—RAID sync failures. After an unclean shutdown caused by a power outage, a NAS running a RAID array will almost always initiate a mandatory consistency check, often referred to as a RAID scrub, resync, or parity check, immediately upon rebooting. Because the system cannot verify if all data was written correctly before the power died, it must meticulously read every single sector of every single hard drive in the array to compare the data against the parity blocks and repair any mismatches.
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The problem is that a RAID resync is actually an incredibly intensive operation that forces the hard drives to run at 100% for many hours or even days, depending on the size of the volume. If your hard drives are aging or have developed minor, dormant mechanical defects, it might just cause one or more of your drives to fail completely.
With RAID 5, where the array can only withstand a single drive failure, losing a drive during a resync leaves the array in a degraded state with no redundancy. If a second drive encounters an unrecoverable read error or fails under the sustained load of the rebuild, the entire storage volume is lost. Yikes.
Thankfully, a UPS prevents this dangerous scenario entirely. By ensuring the NAS always shuts down cleanly, the “dirty bit” flag is never set on the file system. Consequently, when the power returns and the NAS boots up, it knows the array is clean and does not need to perform a punishing parity check. This spares your hard drives from unnecessary wear and tear and avoids the “danger zone” of high-stress recovery operations, significantly reducing the statistical probability of a multi-drive failure event.
A UPS is a must-have for a NAS if you want your drives to live a healthy life, so you might as well get one today, even if you think your power is stable enough to prevent these issues.
