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What is a UPS and what is it for?
A UPS (Uninterruptible Power Supply) is a device that provides backup electrical power when the main supply fails. It acts as a shield between your equipment and the power grid, absorbing outages, micro-cuts and voltage fluctuations.
For a NAS, a UPS is not a luxury — it's critical protection. A power cut during a disk write can corrupt the filesystem, damage a RAID volume, or even make a BTRFS or ZFS pool unrecoverable. A UPS gives you enough time for the NAS to execute its safe shutdown sequence.
There are three types of UPS: standby (basic, switches to battery on failure), line-interactive (continuously regulates voltage, most recommended for home lab), and online double-conversion (full isolation from the grid, for critical environments and production servers).
Have a RAID configured? Combine your UPS with a good storage strategy. Check out our RAID calculator to properly size your array.
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Recommended UPS Models Comparison
| Model | Capacity | Runtime at 100W | Runtime at 300W | Approx. price | Best for |
|---|---|---|---|---|---|
| APC Back-UPS 700VA | 700VA / 405W | ~25 min | ~10 min | ~$99 | basic nas-2bay |
| APC Back-UPS 1000VA | 1000VA / 600W | ~45 min | ~18 min | ~$129 | nas-4bay soho |
| Eaton 5E 1500VA | 1500VA / 900W | ~65 min | ~22 min | ~$175 | nas-4bay workstation |
| CyberPower CP1500EPFCLCD | 1500VA / 900W | ~60 min | ~20 min | ~$169 | nas-4bay soho |
| APC Smart-UPS 1500VA | 1500VA / 1000W | ~180 min | — | ~$599 | rack server enterprise |
Frequently Asked Questions about UPS
How much UPS power do I need for a NAS?
For a 4-bay NAS like the Synology DS923+ (idle ~35W, active ~70W), a 700VA UPS is sufficient if you only connect the NAS. If you add a switch and router, go up to 1000VA. The practical rule: the UPS should have twice the wattage of your maximum consumption.
What is the difference between VA and W in a UPS?
VA (volt-amperes) is apparent power and W (watts) is real power. A 1000VA UPS typically delivers ~600W real power (power factor 0.6). Always calculate your consumption in W and look for a UPS with at least double that figure in VA.
How long does a 1000VA UPS last with a 4-drive NAS?
A 4-bay NAS typically consumes 40–80W in normal operation. A 1000VA UPS (~600W real, ~120Wh battery) would last between 45 and 90 minutes. Enough for several safe shutdown cycles.
Does a UPS protect against voltage spikes as well as outages?
Yes. All UPS units include surge protection. Line-interactive models also regulate voltage against fluctuations. Only online (double-conversion) UPS units offer complete isolation from the power grid.
How often should the UPS battery be replaced?
Sealed lead-acid batteries (most home UPS units) last between 3 and 5 years depending on ambient temperature and the number of discharge cycles. Many UPS units have a warning LED when the battery needs replacement.