Last month my TrueNAS server rebooted mid-scrub during a power flicker that lasted maybe half a second. Nothing dramatic — the lights barely dimmed — but the ZFS pool came back with a degraded vdev and I spent two hours rebuilding. That’s when I finally stopped procrastinating and bought a UPS.
If you’re running a homelab with any kind of persistent storage — especially ZFS on TrueNAS — you need battery backup. Not “eventually.” Now. Here’s what I learned picking one out and setting it up with automatic shutdown via NUT.
Why Homelabs Need a UPS More Than Desktops Do
A desktop PC losing power is annoying. You lose your unsaved work and reboot. A server losing power mid-write can corrupt your filesystem, break a RAID rebuild, or — in the worst case with ZFS — leave your pool in an unrecoverable state.
I’ve been running TrueNAS on a custom build (I wrote about picking the right drives for it) and the one thing I kept putting off was power protection. Classic homelab mistake: spend $800 on drives, $0 on keeping them alive during outages.
The math is simple. A decent UPS costs $150-250. A failed ZFS pool can mean rebuilding from backup (hours) or losing data (priceless). The UPS pays for itself the first time your power blips.
Simulated Sine Wave vs. Pure Sine Wave — It Actually Matters
Most cheap UPS units output a “simulated” or “stepped” sine wave. For basic electronics, this is fine. But modern server PSUs with active PFC (Power Factor Correction) can behave badly on simulated sine wave — they may refuse to switch to battery, reboot anyway, or run hot.
The rule: if your server has an active PFC power supply (most ATX PSUs sold after 2020 do), get a pure sine wave UPS. Don’t save $40 on a simulated unit and then wonder why your server still crashes during outages.
Both units I’d recommend output pure sine wave:
APC Back-UPS Pro BR1500MS2 — My Pick
This is what I ended up buying. The APC BR1500MS2 is a 1500VA/900W pure sine wave unit with 10 outlets, USB-A and USB-C charging ports, and — critically — a USB data port for NUT monitoring. (Full disclosure: affiliate link.)
Why I picked it:
- Pure sine wave output — no PFC compatibility issues
- USB HID interface — TrueNAS recognizes it immediately via NUT, no drivers needed
- 900W actual capacity — enough for my TrueNAS box (draws ~180W), plus my network switch and router
- LCD display — shows load %, battery %, estimated runtime in real-time
- User-replaceable battery — when the battery dies in 3-5 years, swap it for ~$40 instead of buying a new UPS
At ~180W load, I get about 25 minutes of runtime. That’s more than enough for NUT to detect the outage and trigger a clean shutdown.
CyberPower CP1500PFCLCD — The Alternative
If APC is out of stock or you prefer CyberPower, the CP1500PFCLCD is the direct competitor. Same 1500VA rating, pure sine wave, 12 outlets, USB HID for NUT. (Affiliate link.)
The CyberPower is usually $10-20 cheaper than the APC. Functionally, they’re nearly identical for homelab use. I went APC because I’ve had good luck with their battery replacements, but either is a solid choice. Pick whichever is cheaper when you’re shopping.
Sizing Your UPS: VA, Watts, and Runtime
UPS capacity is rated in VA (Volt-Amps) and Watts. They’re not the same thing. For homelab purposes, focus on Watts.
Here’s how to size it:
- Measure your actual draw. A Kill A Watt meter costs ~$25 and tells you exactly how many watts your server pulls from the wall. (Affiliate link.) Don’t guess — PSU wattage ratings are maximums, not actual draw.
- Add up everything you want on battery. Server + router + switch is typical. Monitors and non-essential stuff go on surge-only outlets.
- Target 50-70% load. A 900W UPS running 450W of gear gives you reasonable runtime (~8-12 minutes) and doesn’t stress the battery.
My setup: TrueNAS box (~180W) + UniFi switch (~15W) + router (~12W) = ~207W total. On a 900W UPS, that’s 23% load, giving me ~25 minutes of runtime. Overkill? Maybe. But I’d rather have headroom than run at 80% and get 4 minutes of battery.
Setting Up NUT on TrueNAS for Automatic Shutdown
A UPS without automatic shutdown is just a really expensive power strip with a battery. The whole point is graceful shutdown — your server detects the outage, saves everything, and powers down cleanly before the battery dies.
TrueNAS has NUT (Network UPS Tools) built in. Here’s the setup:
1. Connect the USB data cable
Plug the USB cable from the UPS into your TrueNAS machine. Not a charging cable — the data cable that came with the UPS. Go to System → Advanced → Storage and make sure the USB device shows up.
2. Configure the UPS service
In TrueNAS SCALE, go to System Settings → Services → UPS:
UPS Mode: Master
Driver: usbhid-ups (auto-detected for APC and CyberPower)
Port: auto
Shutdown Mode: UPS reaches low battery
Shutdown Timer: 30 seconds
Monitor User: upsmon
Monitor Password: (set something, you'll need it for NUT clients)3. Enable and test
Start the UPS service, enable auto-start. Then SSH in and check:
upsc ups@localhostYou should see battery charge, load, input voltage, and status. If it says OL (online), you’re good. Pull the power cord from the wall briefly — it should switch to OB (on battery) and you’ll see the charge start to drop.
4. NUT clients for other machines
If you’re running Docker containers or other servers (like an Ollama inference box), they can connect as NUT clients to the same UPS. On a Linux box:
apt install nut-client
# Edit /etc/nut/upsmon.conf:
MONITOR ups@truenas-ip 1 upsmon yourpassword slave
SHUTDOWNCMD "/sbin/shutdown -h +0"Now when the UPS battery hits critical, TrueNAS shuts down first, then signals clients to do the same.
Monitoring UPS Health Over Time
Batteries degrade. A 3-year-old UPS might only give you 8 minutes instead of 25. NUT tracks battery health, but you need to actually look at it.
I have a cron job that checks upsc ups@localhost battery.charge weekly and logs it. If charge drops below 80% at full load, it’s time for a replacement battery. APC replacement batteries (RBC models) run $30-50 on Amazon and take two minutes to swap.
If you’re running a monitoring stack (Prometheus + Grafana), there’s a NUT exporter that makes this trivial. But honestly, a cron job and a log file works fine for a homelab.
What About Rack-Mount UPS?
If you’ve graduated to a proper server rack, the tower units I mentioned above won’t fit. The APC SMT1500RM2U is the rack-mount equivalent — 2U, 1500VA, pure sine wave, NUT compatible. It’s about 2x the price of the tower version. Only worth it if you actually have a rack.
For most homelabbers running a Docker or K8s setup on a single tower server, the desktop UPS units are plenty. Don’t buy rack-mount gear for a shelf setup — you’re paying for the form factor, not better protection.
The Backup Chain: UPS Is Just One Link
A UPS protects against power loss. It doesn’t protect against drive failure, ransomware, or accidental rm -rf. If you haven’t set up a real backup strategy, I wrote about enterprise-grade backup for homelabs — the 3-2-1 rule still applies, even at home.
The full resilience stack for a homelab: UPS for power → ZFS for disk redundancy → offsite backups for disaster recovery. Skip any layer and you’re gambling.
Go buy a UPS. Your data will thank you the next time the power blinks.
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