Part of UPS applications → Home & SOHO storage
What UPS should I buy for a NAS?
Network storage size chart for 2–8 bay Synology, QNAP, and RAID NAS—pick VA first, enable graceful shutdown, then verify backup minutes in the workflow below.
Best for: Home backup, SOHO file servers, and small lab NAS on one protected branch. Not ideal for: Enterprise SAN arrays or stamped data-center designs.
Recommended UPS size for NAS (by bay count)
Quick answer: 2-bay → 650 VA; 4-bay → 1000 VA; 8-bay → 1500 VA (line-interactive with USB shutdown, screening values).
| NAS size | Typical load | Buy this UPS size | Typical backup (screening) |
|---|---|---|---|
| 2-bay (+ router) | ~60–90 W (0.06–0.09 kW) | 650 VA / ~400 W | 15–30 min (graceful shutdown) |
| 4-bay (+ router) | ~100–150 W (0.10–0.15 kW) | 1000 VA / ~650 W | 20–35 min (stock battery) |
| 8-bay (+ switch) | ~180–250 W (0.18–0.25 kW) | 1500 VA / ~900–1050 W | 25–45 min (stock battery) |
| Rack NAS 12–16 bay | ~300–450 W | 3000 VA+ | External battery if 60+ min |
Which UPS for your NAS deployment?
Purchase decision by how the NAS is used—not only bay count. Match topology, USB shutdown, and battery chemistry to your backup policy.
| Deployment | Typical NAS | Recommended UPS | Topology | Shutdown / battery |
|---|---|---|---|---|
| Home backup | 2–4 bay Synology / QNAP | 650–1000 VA | Line-interactive | USB graceful shutdown; stock VRLA |
| Home lab / media | 4–8 bay + switch | 1000–1500 VA | Line-interactive | Longer Ah if torrents or scrub jobs run on battery |
| Small office file server | 4–8 bay + firewall | 1500 VA | Line-interactive or online | 30–60 min policy; confirm kW headroom |
| Noisy utility / 24×7 sync | Any bay count | Per measured load | Online double-conversion | Minimize transfer gap during active sync |
When to choose online UPS: Frequent voltage sag, heavy cloud sync during outages, or workloads that cannot pause during line-interactive transfer.
NAS UPS buying checklist
Complete before purchase—screening ranges are not product endorsements.
- USB shutdown port compatible with your NAS vendor (Synology/QNAP/TrueNAS)
- Steady watts measured with all HDDs/SSDs spinning (not idle datasheet)
- Spin-up headroom ~20–30% above steady kW for simultaneous disk start
- Router/switch on same UPS if remote management must survive outages
- Graceful shutdown tested—battery test from vendor UI after install
- Backup minutes policy defined (shutdown-only vs 30–60 min ride-through)
- Manufacturer runtime chart checked at your kW, Ah, and age derate
NAS UPS sizing workflow
Four steps from storage load to verified backup minutes. Runtime presets are the last step—not the starting point.
-
Measure NAS load
Sum NAS, HDD/SSD draw, router, and optional switch watts on the protected branch.
UPS Load Calculator -
Pick UPS size (kVA)
Convert kW to kVA with power factor (~0.8 for mixed IT/NAS) and add headroom for disk inrush.
UPS Capacity Calculator -
Size battery Ah
Enter target backup minutes and battery voltage—size for graceful shutdown or longer ride-through.
UPS Battery Calculator -
Verify NAS backup time
Confirm minutes at your measured kW, UPS kVA, and Ah. Open a bay-count preset:
RAID, disks, and NAS steady power
RAID level changes rebuild stress and how many spindles spin—not always higher steady watts. What matters for UPS sizing is how many drives are active during your heaviest workload (scrub, rebuild, backup).
| Component | Typical power | Notes |
|---|---|---|
| 2-bay NAS chassis (no disks) | 15–25 W | ARM or low-power CPU |
| 4-bay NAS (4 × HDD) | +32–40 W disks | ~8–10 W per 3.5″ HDD steady |
| SSD pool | Lower per drive | Higher burst on sync jobs |
| 10 GbE add-in / NIC | +5–12 W | When link active |
| Router / firewall | 10–20 W | Often on same UPS as home NAS |
Synology and QNAP publish per-model power—use their calculator with your exact drives. BTRFS and ZFS scrub jobs can keep disks busy for hours; size battery minutes if you must not interrupt those tasks during outages.
Graceful shutdown and USB signaling
Most Synology and QNAP units support UPS USB or serial signaling—when remaining battery crosses a threshold, the NAS flushes caches and powers down disks safely. Enable vendor UPS support and run a test outage after install.
- USB shutdown: Preferred for tower UPS under the desk or in a closet.
- Network-managed UPS: Requires switch and management path to stay up—often same UPS feeds NAS and switch.
- PowerChute / vendor daemons: Some APC and CyberPower models need their agent on a separate PC unless the NAS supports native USB.
Example: 2, 4, and 8-bay NAS roll-ups
| System | NAS | Disks | Router | Total (approx.) |
|---|---|---|---|---|
| 2-bay home | 20 W | 2 × 8 W = 16 W | 15 W | ~51 W |
| 4-bay SOHO | 35 W | 4 × 9 W = 36 W | 18 W | ~89 W |
| 8-bay lab | 55 W | 8 × 9 W = 72 W | 25 W switch | ~152 W |
Key variables for NAS UPS
- HDD spin-up vs steady draw: Size on measured active watts; add headroom for simultaneous spin-up.
- RAID rebuild / scrub: Disks stay busy longer—battery minutes must cover policy or trigger shutdown early.
- Remote access path: If users need VPN during outages, include router and switch on the UPS.
- SSD vs HDD pools: SSDs lower steady W but sync bursts can still matter for Ah.
- Cabinet temperature: Closet heat ages VRLA faster—derate expected minutes.
Common NAS UPS sizing mistakes
- Sizing on idle NAS watts — active disks and network jobs run higher.
- No USB shutdown configured — battery dies mid-write and corrupts volumes.
- UPS only on NAS, not router — cannot manage shutdown remotely during outage.
- Ignoring spin-up inrush — UPS overload alarm on power return when all disks restart.
- Expecting hours on stock battery — home NAS UPS targets graceful shutdown, not multi-hour runtime.
UPS battery sizing for NAS
Many home NAS policies need only 10–30 minutes—enough for graceful shutdown—not full business continuity. Enter load and target minutes in the battery calculator, then verify in step 4 presets.
Example: 0.15 kW (4-bay) on 1 kVA / 48 V 100 Ah often screens 25–40 minutes before age derate—sufficient for USB shutdown thresholds around 20% battery.
Assumptions and disclaimer
Figures are planning estimates (efficiency ~0.8, safety factor ~0.7). Battery age, temperature, and disk workload change real minutes. VA ranges are screening only—not product endorsements. Confirm with manufacturer charts and your IT policy.
Related guides
Frequently asked questions
What size UPS for a 4-bay NAS?
Screen roughly 80–150 W steady load (4-bay NAS + router on the same UPS). A 1000 VA / 650 W line-interactive UPS with USB shutdown is a common home and SOHO starting point—confirm with measured watts and your backup policy.
Should a NAS be on a UPS?
Yes for most installs—sudden power loss during writes can corrupt RAID volumes or BTRFS pools. A UPS provides ride-through and, with USB signaling, triggers graceful shutdown before battery exhaustion.
How long should a NAS stay on battery?
Home users often target 10–30 minutes for graceful shutdown and brief outages. Small offices may need 30–60 minutes if no generator—size Ah to policy, not a generic default.
Does RAID increase UPS load?
RAID mainly affects how many disks spin—more HDDs mean higher steady watts and higher spin-up inrush. Size on measured draw with all drives active, not idle datasheet values.
Synology vs QNAP power draw?
Both publish per-model watts in datasheets. 2–4 bay units often screen 25–60 W steady; 8-bay rack models can exceed 80 W before disks. Always meter your configuration with drives installed.
Can one UPS feed NAS and router?
Common for home labs—sum NAS, router, and optional switch watts on one branch. Ensure total kW fits UPS output watts at your site power factor.
Do I need online UPS for NAS?
Line-interactive UPS with AVR covers most home and SOHO NAS. Online double-conversion helps when input power is noisy or you cannot tolerate any transfer gap during recording-heavy workloads.
What about NAS HDD spin-up current?
Staggered spin-up reduces inrush, but simultaneous disk start can briefly spike load. Add 20–30% headroom above steady kW when picking VA—do not size on idle watts alone.
USB shutdown vs network shutdown?
USB from UPS to NAS is the most reliable path for Synology/QNAP graceful shutdown. Network shutdown depends on switch and management path staying up—often both NAS and switch share one UPS.
Lithium vs VRLA for NAS UPS?
Stock tower UPS use VRLA—fine for closet installs. Hot environments favor lithium packs only when the UPS or external cabinet is rated for that chemistry.
Related UPS scenarios
- UPS for home office — Work-from-home desk + NAS branch planning
- UPS for gaming PC — Game library on the same desk branch
- UPS for CCTV — NVR and PoE on the same branch
- UPS for network closet — Switches feeding your NAS VLAN
- UPS for server rack — Rack NAS and larger storage
- UPS for laboratory — Instrument data paths