Please stop running your home NAS without a UPS (it’s not just about power outages)
Your NAS is probably one of the most expensive pieces of equipment you own, and it stores hundreds of gigabytes of valuable memory and files.
So why is this not connected to a UPS? Let me tell you why not having one is a horrible idea.
The obvious: it protects you from power outages
The main reason you should get one is the same one you were thinking about when you opened this article: power outages. This is the most dramatic and visible threat to data integrity, but many underestimate exactly what happens mechanically and digitally during a sudden loss of power. Keep in mind that a NAS isn’t just a hard drive enclosure; it is a complex server running a specialized operating system that constantly manages file tables, logs, and cached data in the system’s RAM. When you initiate a standard shutdown, the operating system meticulously shuts down running processes, flushes data from volatile RAM to non-volatile storage, and signals the mechanical drive heads to park safely.
Without a UPS, the immediate loss of power prevents hard drive read/write heads from parking properly, which can result in physical damage to platters on older drives or significant wear on modern drives. More importantly, any data temporarily held in the write cache (data that the system “says” has been written but has not yet reached the magnetic platter) is instantly vaporized. Completely disappeared. This is how temporary storage works. This discrepancy often leads to file system corruption, where the drive’s directory structure no longer matches the actual data stored, resulting in “orphan files” or completely unreadable volumes.
I built a low power NAS from a Raspberry Pi
NASberry Pi.
A UPS solves this problem. I’m not saying that it necessarily requires the server to continue running for hours during a power outage, but it will provide a window of time (usually just a few minutes) for the NAS to detect the power outage via a USB data cable. Once detected, the UPS software initiates a graceful, automated shutdown sequence. This ensures that all caches are flushed to the disk, the file system is systematically unmounted, and the hardware shuts down exactly as the manufacturer intended, thereby preserving the physical health of the disks and the logical integrity of the data they contain.
It protects your NAS from dirty energy
A complete outage is a binary event: power is either on or off, but your electrical network also subjects sensitive electronic devices to a spectrum of irregularities known collectively as “dirty electricity.” Wall outlets rarely provide a perfect, consistent voltage of 120 or 230 volts. Instead, the power supply is often affected by voltage sags, sags, frequency noise, and high voltage spikes. A NAS is filled with delicate microprocessors, RAM modules, and disk controllers that rely on a stable voltage to operate at specific frequencies. And when the input voltage fluctuates significantly, the NAS’s internal power supply (PSU) must work overtime to rectify the current, leading to increased heat generation and premature component failure.
Voltage sags are particularly insidious for storage devices. When voltage drops below standard levels, electronic components often attempt to draw more current (amperage) to compensate and maintain the same power output. This power surge creates excessive 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 cuts off the tops of the high voltage spikes but does nothing to increase the low voltage.
A decent line-interactive UPS helps alleviate this problem with a feature called automatic voltage regulation (AVR). The AVR allows the inverter to continuously monitor the incoming voltage. If the voltage drops too low (sag) or rises too high (surge) without actually shutting down, the inverter uses an internal transformer to increase or reduce the voltage to safe levels without switching to battery power. This ensures that the NAS receives a clean, coherent sine wave (or simulated sine wave) of power. Thus, extending its lifespan. Pretty cool.
It protects you from writing holes
If you don’t know what a “write hole” is, it’s a specific and dangerous failure mode associated with RAID configurations, especially those that use parity, such as RAID 5 or RAID 6. These RAID levels work by deleting data on multiple drives and calculating a mathematical checksum, or parity block, that allows the array to rebuild the data if a drive fails.
For each data written, the system must write the data itself and then update the corresponding parity information. These two actions are supposed to happen simultaneously, but in reality they are sequential operations that essentially happen consecutively. If a power failure occurs in the precise millisecond between writing new data and updating the parity block, the array enters an inconsistency state. The data on the disk stripes no longer matches the mathematical parity that is supposed to protect it, resulting in a write hole.
The worst part, however, is that the RAID controller may not immediately realize the error. The tape appears valid until you try to read that specific block or try to rebuild the array after a disk failure. At that point, the controller relies on parity to reconstruct the missing data, but because the parity information is “dirty” or obsolete relative to the unfinished write, the reconstruction will fail or produce corrupt gibberish.
Using a UPS is the most effective hardware defense against write hole phenomenon for consumer and small business NAS units that lack expensive battery-powered write cache controllers. As we told you, it ensures a continuous flow of energy to your NAS, including during the write operation, ensuring that the transaction (writing data and parity) always completes successfully. Even if the lights go out in the building, the UPS maintains voltage long enough for the RAID controller to complete 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 prevents RAID sync failures
Last, but not least, it helps solve another RAID problem: RAID sync failures. After a hard shutdown caused by a power outage, a NAS running a RAID array will almost always initiate a mandatory consistency check, often called a RAID wipe, resync, or parity check, immediately after restarting. Since the system cannot verify whether all data was written correctly before the power was lost, it must meticulously read each sector of each hard drive in the array to compare the data to the parity blocks and repair any inconsistencies.
Please stop putting desktop hard drives in your NAS
Don’t start your NAS journey on the wrong foot.
The problem is that a RAID resync is actually an incredibly intensive operation that requires hard drives to operate at 100% for several hours or even days, depending on the size of the volume. If your hard drives are aging or have minor, latent mechanical defects, this may simply result in the complete failure of one or more of your drives.
With RAID 5, where the array can only withstand a single disk failure, losing a disk during a resync leaves the array in a degraded state, with no redundancy. If a second drive experiences an unrecoverable read error or fails under the sustained load of rebuilding, the entire storage volume is lost. Yeah.
Fortunately, a UPS completely prevents this dangerous scenario. Ensuring that the NAS always shuts down cleanly, the “dirty bit” flag is never set on the file system. Therefore, when power returns and the NAS boots up, it knows that the array is clean and does not need to perform a rigorous parity check. This saves your hard drives from unnecessary wear and tear and avoids the “danger zone” of high-stress recovery operations, thereby significantly reducing the statistical probability of a multiple drive failure event.
A UPS is essential for a NAS if you want your drives to live a healthy life, so you might as well buy one today, even if you think your power supply is stable enough to avoid these problems.
