Sizing CCTV storage, PoE and Wi-Fi for a school with 16 cameras and unreliable power
A government higher secondary school is installing 16 fixed IP cameras (1080p, H.265, quoted at a constant 4 Mbps each, recording 24x7) across corridors, the exam hall and the playground, to be viewed from the headmaster's office and by 20 district-level accounts. The quotation includes a 24-port switch with a 370 W PoE budget, an 8-bay NVR, and four 4 TB surveillance hard disks configured as RAID 5. The headmaster has been told the school must retain 'at least one month of footage'. The school also wants campus Wi-Fi for 200 students and 14 teachers on a 100 Mbps fibre line. Power fails six to eight times a week. The NVR and switch currently sit on one 600 VA desktop UPS, and the fibre router is on no UPS at all.
1. Calculate the storage requirement and judge whether the quoted four-disk RAID 5 configuration meets the one-month retention requirement.
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Size first, buy second. One camera at 4 Mbps is 0.5 MB/s, which is 0.5 x 86,400 = 43,200 MB, about 43.2 GB per day, if recording is genuinely continuous. Sixteen cameras give 691 GB per day, and 30 days give about 20.7 TB of raw footage.
Four 4 TB disks in RAID 5 give (4 - 1) x 4 TB = 12 TB usable, so the quoted build holds roughly 12,000 / 691 = 17 days, not a month: short by about 40%, and that is before filesystem overhead and the fact that surveillance drives should not be filled past about 90%.
Options: eight 4 TB disks in RAID 6, giving 6 x 4 = 24 TB usable and surviving two simultaneous failures; or six 8 TB disks in RAID 5 for 40 TB raw and 32 TB usable, leaving headroom for two more cameras. Or attack the data rather than the disks: enable motion or line-crossing detection on corridors and the playground (typically a 30-40% cut on outdoor scenes), keep the exam hall continuous, and drop the playground to 2 Mbps at 15 fps. That alone can take 20.7 TB below 14 TB.
Note that RAID is availability, not backup. A deleted or corrupted recording is gone across all disks, so export and store exam-hall footage separately, since that is what an inquiry will demand.
2. Check the PoE budget and the backup power arrangement, and state what should change.
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PoE: 16 cameras at about 8 W each (check the datasheet, 1080p IR units are commonly 6-12 W) is 128 W, plus two access points at 15 W is 158 W, comfortably inside the 370 W switch budget. Confirm the per-port allocation and that Cat 6 runs stay under 100 m, because at 90 m or more the voltage drop can make a camera reboot at night when the IR illuminators switch on.
The real problem is the UPS. A 600 VA desktop unit is typically rated around 360 W and holds one 12 V, 7-9 Ah battery, roughly 84-108 Wh; at 0.8 depth of discharge and 0.85 efficiency that is only 57-73 Wh usable. With the NVR at about 60 W and the switch plus PoE load at about 160 W, the total is roughly 220 W, giving 15-20 minutes: enough for a clean shutdown, nowhere near riding out six to eight outages a week, and a hard cut mid-write is exactly how surveillance file systems get corrupted.
Change: move the NVR, switch and fibre router onto a proper inverter or online UPS sized for at least one hour, put the router on it too (currently unprotected, so every outage also kills Wi-Fi and remote viewing), configure the NVR to shut down gracefully at a defined battery level, and test the runtime under real load rather than trusting the box label.
3. Advise on the campus Wi-Fi design and on securing the 20 remote camera-viewing accounts, explaining the specific risk each measure addresses.
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Wi-Fi: 200 students sharing 100 Mbps is 0.5 Mbps each if everyone is active, so the goal is coverage, fair sharing and control, not headline speed. One router with four LAN ports will not cover a school. Plan four to six access points on 5 GHz with a controller, budgeting roughly 30-40 active clients per AP, and enable band steering. Split the network into separate SSIDs and VLANs: staff, students (captive portal plus content filtering, since the school is responsible for what minors reach), and cameras.
Leaving cameras on the flat LAN or the student SSID lets any student open the NVR's web page. Never port-forward the NVR to the internet so 20 district accounts can watch: that exposes it to the whole internet and to default-credential scans. Use the vendor's P2P service with a strong unique password and multi-factor authentication, or a VPN, and set lockout after repeated failures. Give each district user their own account rather than a shared one so footage views can be attributed, and change every camera's default password at installation.
Two more points: keep camera firmware updated, and treat recordings as personal data. Corridor and playground video of minors is precisely what a data-protection review will ask about, so restrict who can export clips and log every export.