Should NAS be paired with a UPS? The night RAID rebuilt to 62%, the switch tripped; I checked both power calculation and auto shutdown settings

Last August, when I was rebuilding RAID and the progress bar had climbed to 62%, the air conditioner compressor started up, the distribution box clicked, and the whole house went black. The next day, I called: the rebuild progress had reset to zero, and 11 hours of waiting were wasted. That day, I put the UPS in my shopping cart.

to be clear, UPS isn't about power outages, but about the outage

many people think that if their homes don't lose power a few times a year, UPS systems are simply a waste of money. I used to think so too. Only after actually running a NAS do you realize that what you fear isn't a "power outage," but that moment you might just hit something during the outage.

a normally functioning NAS loses power, it's very likely fine. file systems like ext4 and Btrfs all have logs. Next time you boot up, you can fix the file system yourself, at most just lose the last few seconds of data you're writing. The real deadly moments are two.

first, the head is writing to the disk. The magnetic head of a mechanical disk floats on the plate, and the electromagnetic head cannot return in time, which theoretically poses a physical risk. Once or twice occasionally, it's usually fine; if too often, it's just a gamble. how hard drive bad sectors accumulate are built up from repeated minor damage.

second type, the one I ran into — a RAID rebuild that lost power halfway through. Rebuilding reads each sector from the source disk and writes it to the new drive; if interrupted, you have to start over. If luck is worse, the source drives are already under high load during reconstruction, and if another hard power cut occurs, both disks will fail and the data will be lost. in the article I wrote about how to choose RAIDs I said you have to control during downgrades. You can't handle power outages, so you have to rely on the UPS to cover for it.

there's a hidden issue: in summer, when the air conditioner starts up, the voltage drops during thunderstorms—sometimes just a fraction of a second, and the NAS restarts once again. It flashes more than a dozen times a year, causing both the power supply and motherboard to lose their lifespan.

first step is to calculate power—don't just copy the office formula

searching for "NAS UPS recommendations," most of the results are about data center approaches, often starting at 1KVA. If you really can't use it for home use, first calculate your own power.

my N100 mini PC runs dual drives on Flying Bull. I tested it in a on electricity bills: 11W for sleep, 17W for light load, 26W for read/write, and only 31W for transcoding under full load. A machine with four trays fully equipped with mechanical discs is about 40 to 50 watts.

another easily missed point: the optical modem and main router must also be connected to the UPS. Otherwise, if the mains power goes out, the network dies first, and you can't even see the NAS status when you're outside, which is like being protected in isolation. The optical modem ranges from 12 to 15 watts, and the main router uses 8 to 12 watts.

When choosing

, don't just look at VA rating—just look at the nominal wattage. VA multiplied by power factor is the wattage. Some machines are labeled as 600VA but actually only provide 300W, so misreading it can cause problems. My top setup is 70W, and the 600VA/360W machine has plenty of spare space.

to buy: understand these three parameters and avoid pitfalls

first, type. A household backup is enough—normally, mains power is directly connected, switching between 2 and 10 milliseconds after power outage, and NAS switching power supplies have large capacitors that can easily withstand those tenths of a second. Online interactive systems now have voltage stabilization, which is useful in old residential communities where voltage has been fluctuating all year round. Online is zero switching, used in data centers, and buying for home use is a waste of money.

the second waveform. Backup models mostly simulate sine waves, and some online say it damages the power supply. My UPS simulating sine wave has been running for two years, and the NAS power supply has never had any issues. If you really have a cleanliness freak and add pure sine wave waves, the price will instantly double. Whether it's worth it or not, you have to weigh it yourself.

third, and most critical one: must have a USB communication port . This is the lifeblood of automatic shutdown when the power is cut off. A UPS without a communication port is just a big battery—when the power goes off, it just keeps powering without thinking, and the NAS doesn't even realize the mains power is gone. Running around until the battery runs out and forcing a shutdown is basically a wasted purchase. Before ordering, search for "USB monitoring" or "communication port" on the parameter page; if you can't find it, just pass. Mainstream models like APC's BK series and Santak's TG-BOX series are included, priced between 300 and 500 yuan.

Also, remember that batteries are consumables. Lead-acid batteries inevitably degrade every 3 to 5 years, and replacing a battery will cost around a hundred yuan. So don't buy models that are too niche, or you won't be able to find a battery replacement in three years.

Synology set it this way: three check and one must not be missing

USB cables connect the UPS and NAS, and Synology can recognize it in the control panel→ hardware and power supply → uninterruptible power supply system . In the old DSM version, this tab was called UPS, and the components were the same.

check off three places one by one:

• enable UPS support, select "USB UPS" as the type
• "Power off the system after entering safe mode"—this is the core. Safe mode means Synology first stops all services, uninstalls storage space, safely returns the head, and then executes shutdown. This is what a clean shutdown means. "Enter safe mode when battery is low
• double protection, just in case the previous step isn't triggered

then go to the hardware and power → regular and check "Auto restart after power outage" as well. After powering on, the NAS powers on automatically, so you don't have to go back and press the power button.

time, I set it to wait 5 minutes after the power cut before entering safe mode. Don't set it too short—in summer, a voltage flash triggers shutdown, and restarting is even more damaging than cutting off power itself.

Feiniu set it like this: after 0.8.27, it's free to give away

Feiniu fnOS added native UPS functionality in version 0.8.27 (December 2024), running the standard NUT protocol, and the USB UPS can be recognized as soon as you plug in. Upgrade the older version first; the system settings will have a UPS entry point.

three parameters, say

• TIMEOUT: How many seconds after a mains power outage does it activate? The default 0 means it starts running immediately when it drops. I set it to 60 seconds to prevent false shutdowns from voltage flashes.
• BATTERYLEVEL: If the UPS battery level drops below this threshold, it will shut down. I set 80
• MINUTES: If the UPS battery doesn't last this minute, it will start shutting down, giving enough time for the shutdown process

a self-assembled machine (like my N100 mini PC), there's another step: go into the BIOS and find "Restore AC Power Loss" or "Power Start" and set it to Power On. If the UPS starts automatically without power, it only protects half of it—shutting it off is safe, but when power comes in, you still have to manually turn it on.

range, rehearsals, and two easily missed

once it's ready, don't just let it go. unplug the power system once for a drill . I just pulled the UPS plug: as soon as the buzzer sounded, the NAS switched to safe mode and shut it off after 5 minutes, the optical modem and router were still running on the UPS, and my phone could access the internet normally. Only after going through the entire process can you feel confident.

range is more generous than expected. With a 70W load and a 600VA machine, I tested it for 47 minutes—because the NAS shuts down safely midway, leaving everything behind for the optical modem to handle. If you really care about range, look at the battery capacity in Ah, not just the VA.

After

power startup, the Docker containers I installed also started up, so I didn't have to click them one by one. Docker the basic mentioned container restart strategies. Some containers were set to not auto-start at the time, so remember to check them out after practice.

the first thing you might overlook: don't have a UPS, don't open SSD read/write caches . The logic of read-write caches is to store disk actions in the cache and place them at the right moment. If the power is cut off and the cache trips, the cache data is not logged, directly damaging the file system. This is where the cache and UPS bind die.

the second item prone to leakage: the UPS is not a surge protector. Its surge protection can't withstand direct lightning strikes, so you still have to unplug the plugs you need during thunderstorms. It only cares about the power outage, not the heavens.

finish with a clear order: first calculate the power, then choose a model with a USB communication port. Synology sets all three checkboxes, Feiniu TIMEOUT is set to 60 seconds, the assembled PC remembers BIOS to start automatically when powered on, and finally unplugging the mains power for a drill. What took half an hour was no longer having to worry about progress bars in the pitch-black room.