This article answers a very specific question that almost nobody in the market explains clearly: given how many cameras I have now, when should I upgrade from SD card recording to an NVR? All figures below are calculated using actual models available in our store, with prices read in real time.
1. First, distinguish the two layers: power supply vs. recording
The point most people confuse is treating a “PoE switch” and an “NVR” as either-or choices. In fact, they perform completely different jobs:
| PoE switch (such as RLA-PS1E) | NVR (such as NVS4-NHD) | |
|---|---|---|
| What it does | Power supply ＋ data transmission | Centralized recording ＋ centralized playback |
| Hard drive included? | No | Yes (optional on some models) |
| PoE ports? | Yes (RLA-PS1E has 4) | Some models do (NVS4 has 4) |
| Impact on functionality | None (network-only device) | Takes over recording and some smart features |
| Price | HK$399 | From HK$830 |
2. The real limitations of an SD card setup
First, let’s clarify what SD card recording can do. Assuming 2K (4MP) H.265 at approximately 4Mbps—which is the typical bitrate for most 2K cameras in our store—each camera uses approximately 43GBper day.
| Number of cameras | Total daily write volume | Storage capacity of a 512GB card | Notes |
|---|---|---|---|
| 1 camera | 43GB | Approximately 12 days | Loop recording; sufficient for reviewing recent footage after an incident |
| 2 cameras | 86GB | Approximately 6 days | Starting to become impractical |
| 4 cameras | 173GB | Approximately 3 days | Only three days, with almost no room to review footage |
| 8 cameras | 346GB | Approx. 1.5 days | Not feasible |
Note that this calculation assumes “one card per camera, each operating independently”. 512GB is already the practical limit for microSD; even more expensive cards will not be larger.
3. The cost break-even point is the 3rd camera
Let’s calculate the costs clearly. A 512GB high-endurance microSD card costs approximately HK$450; a surveillance-grade 2TB hard drive costs approximately HK$500, while a 4TB drive costs approximately HK$700.
| Number of cameras | All SD cards (512GB × N) | NVS4-NHD ＋ hard drive | Difference |
|---|---|---|---|
| 1 camera | HK$450 | HK$1,330 | SD cards cheaper by HK$880 |
| 2 cameras | HK$900 | HK$1,330 | SD cards cheaper by HK$430 |
| 3 cameras | HK$1,350 | HK$1,330 | Break-even |
| 4 cameras | HK$1,800 | HK$1,530 (4TB) | NVR cheaper by HK$270 |
The difference becomes even more obvious when you look at retention days: 4 cameras with SD cards provide only 3 days, while the NVS4 with 4TB provides 23 days. For the same amount of money, one gives you three days, while the other gives you three weeks.
Three practical options
If you already know you need an NVR after reading the calculations above, these three models are the corresponding answers:
| Model | Price | Suitable for |
|---|---|---|
| Reolink NVS4-NHD 4-channel PoE | HK$830 | Up to 4 cameras, the most common setup |
| Reolink NVS8-NHD (built-in 2TB) | HK$2,599 | 8 cameras, for those who do not want to research hard drives separately |
| Reolink NVS36 36-channel | HK$1,899 | 17 cameras or more,requires a separate PoE switch |
4. Three Things an NVR Does That Cannot Be Replaced (It’s Not About Money)
If you only look at the price, you can make your decision here. But there are three things that the price table cannot reflect, and they are the real reasons people regret their choice.
1. One Timeline
With 4 cameras recording to cards, you have 4 separate timelines. If you want to check “who walked past the back alley at 11 p.m. last night,” you have to log in to each camera, drag through each timeline, and compare the times yourself. If even one camera’s clock is off by a few minutes, you may end up investigating in the wrong direction.
An NVR gives you one timeline with four synchronized views. At the same point in time, you can see all four angles together—this is the key difference for providing evidence and managing your business day to day, and it is why so many store owners say “I should have switched sooner” after upgrading.
2. Silent Failure: You Won’t Know When the Card Fails
This is the most insidious issue and the one people talk about the least. When a microSD card fails, the camera itself is still working—the app continues to show “Running,” live view still works, and push notifications are still sent.The only thing that has failed is recording.
You will not receive any warning. Three months later, when something happens, you open playback and discover that the card actually stopped working last month, leaving a complete gap in the footage.
Typical symptoms include the playback timeline suddenly becoming completely blank after a certain date; the card switching to read-only mode so new recordings cannot be written; or damaged sections appearing in the loop-overwrite area, making clips impossible to play. None of these issues are obvious in the mobile app.
3. Capacity Can Be Expanded; Cards Cannot
NVS4 has 1 SATA port, supporting up to 6TB. NVS8 has 1 SATA ＋ 1 eSATA port, supporting up to 12TB. NVS36 has 3 SATA ports, supporting up to 48TB. Hard drives can be replaced with larger ones or additional drives can be added as needed. There is only one microSD slot, with a maximum capacity of 512GB.
5. Capacity Formula: Calculate It Yourself
The most common mistake when buying an NVR is buying the main unit but not enough hard drive capacity. Calculate it yourself using this formula:
Retention days ＝ Hard drive capacity (GB) ÷ Daily capacity
(1Mbps of continuous recording for 24 hours ≈ 10.8GB. 2K H.265 is approximately 4Mbps, and 4K approximately 8Mbps.)
| Scenario | Total bitrate | Per day | Required for 30 days |
|---|---|---|---|
| 4 × 2K | 16Mbps | 173GB | 5.2TB |
| 4 × 4K | 32Mbps | 346GB | 10.4TB |
| 8 × 2K | 32Mbps | 346GB | 10.4TB |
| 8 × 4K | 64Mbps | 691GB | 20.7TB |
| 16 × 2K | 64Mbps | 691GB | 20.7TB |
Compare this with the model limits: NVS4 supports up to 6TB (approximately 34 days for 4 × 2K), NVS8 supports up to 12TB (approximately 34 days for 8 × 2K), and NVS36 supports up to 48TB (approximately 69 days for 16 × 2K).To retain 16 × 4K footage for 30 days, even 48TB is only just enough.
6. The Cross-Brand Trap: An NVR Is Not a Case of “If It Fits, It Works”
This section is crucial when deciding which NVR to buy.
| Combination | Feature loss | Reason |
|---|---|---|
| Same-brand camera + same-brand NVR | None | Designed by the original manufacturer; AI detection, notifications, and playback all work natively |
| Any-brand camera + PoE switch | None | The switch does not participate in any features; it only supplies power |
| Cross-brand camera + NVR | Some | Relies on ONVIF／RTSP; pan-tilt control and AI detection will mostly be unavailable |
Take EZVIZ H8C PoE connected to Reolink NVS4 as an example: the video feed can be displayed (via ONVIF), but features such as 350° pan-tilt rotation, automatic tracking, and person detection notifications—the “reasons for buying a pan-tilt camera”—will mostly only be available in the EZVIZ app. Reolink’s official page also states that it “supports RTSP／RTMP and can theoretically connect to third-party ONVIF／RTSP cameras, but compatibility and features (such as AI detection) are not guaranteed.”
7. Four Scales, Four Answers
| Your situation | The right approach | Reason |
|---|---|---|
| 1 camera, already purchased | microSD 512GB | Cheapest option; an NVR costs more than twice as much |
| 2 cameras, same brand | microSD ×2 | Still cheaper than an NVR |
| 3 cameras | It’s a tie | Depends on whether you want a single timeline |
| 4 or more cameras, new installation | Buy an NVR + same-brand cameras directly | Power and recording are handled by one device, with no feature loss |
| Already renovated, do not want to run power cables | NVR（PoE）or Wi-Fi NVR | A PoE NVR supplies power and data over a single network cable |
The last row deserves further explanation: if your renovation is already complete, the ceiling has been sealed, and you do not want to run additional power cables, the value of a PoE NVR suddenly becomes much greater—because each camera only needs a single network cable, so you do not need to find a power outlet at every location. This difference in installation cost is often greater than the price difference between the devices.
8. Frequently Asked Questions
I bought a PoE switch. Do I still need an NVR?
It depends on the number of cameras. For 1–2 cameras, you do not need one; a memory card is enough. For 4 or more cameras, you do—and at that point, you should buy an NVR with built-in PoE ports directly, making the switch unnecessary.
Does an NVR have to be paired with cameras from the same brand?
Technically, cross-brand setups are possible (ONVIF／RTSP), but pan-tilt control and AI detection will mostly be unavailable. Using the same brand is strongly recommended.
Will I receive a notification if the microSD card fails?
Most models will not send one. The camera will continue operating and displaying video, but recording will stop silently. This is the biggest risk of using a memory card.
How many days can a 512GB card record?
Approximately 12 days for 1 2K camera, or 3 days for 4 2K cameras. Formula: GB per day ＝ total bitrate × 10.8.
Can an NVR start recording immediately after I buy it?
It depends on which model you purchase. Hard drives must be purchased separately for models such as the NVS4-NHD; the NVS8 includes a built-in 2TB drive, the NVS16 includes a built-in 4TB drive, and the KIT bundles already include hard drives, so you can start recording right out of the box.
Can I use a regular desktop hard drive?
Technically, yes, but recording involves continuous 24/7 writing. A surveillance-grade hard drive is recommended; otherwise, there may be risks to its lifespan and warranty coverage.
Can I add a hard drive later?
Yes. The NVS4 has 1 SATA port, the NVS8 has 1 SATA + 1 eSATA port, and the NVS36 has 3 SATA ports. You can add drives up to the supported limit.
What happens during a power outage?
The NVR and all cameras will stop operating. To keep the system running, you need to add a UPS, and both the NVR and the switch/cameras must be connected to the UPS.
9. Further Reading
- How to Choose from the 13 NVRs in Our Store——A tiered comparison of 4-channel, 8-channel, 16-channel, and 36-channel models
- EZVIZ H8C + Reolink Switch Tested in Practice——The actual setup for a single camera
- How to Choose PoE Power Supply and an NVR——Three formulas for power budget, bandwidth, and hard drives
- WiFi Cam or PoE Cam——Four power supply methods