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Retention is usually discovered at the worst possible moment — an incident surfaces three weeks late and the footage has already rolled over. Storage is the cheapest part of a system to get right at design and the most expensive to fix afterward.
Cambridge is an automotive manufacturing centre, and the tier-one and tier-two suppliers clustered around it operate under customer security requirements that are frequently more demanding than anything the business would specify for itself. Intellectual property protection around tooling and process is a real concern, which puts weight on interior access control and on knowing precisely who was in a given area at a given time.
OEM-imposed security requirements and process IP protection. Interior zone control and access audit trails usually outrank perimeter coverage.
One megabit per second of sustained video is 10.8 GB per day. Everything after that is multiplication.
| Scenario | Bitrate per camera | Cameras | Retention | Raw storage |
|---|---|---|---|---|
| Small commercial, H.265 | 4 Mbps | 8 | 30 days | 10.4 TB |
| Warehouse, H.265, 4K at docks | 8 Mbps | 24 | 60 days | 124 TB |
| Construction site, motion only | 6 Mbps | 6 | 90 days | 35 TB |
| Distribution centre, H.264 | 12 Mbps | 48 | 90 days | 560 TB |
Insurers, agreements with shippers and client contracts frequently specify a minimum retention period, and some carry a duty to preserve footage once an incident is reported. Check what you have already agreed to before choosing a number — it is usually longer than the 14 or 30 days a recorder ships configured for.
Rebuilding a RAID 5 array reads every sector on every remaining drive. On a large array that read volume approaches the published unrecoverable-read-error rate of consumer drives, and a second fault during the rebuild loses the array. Use RAID 6 or RAID 10 above roughly 12 TB — and treat RAID as uptime protection rather than backup. It does nothing about the recorder being stolen, which on a construction site is the realistic threat.
Desktop drives are specified for roughly 55 TB of writes a year and for substantial idle time. A surveillance recorder writes continuously from every camera and never idles. Surveillance-rated drives carry far higher annual workload ratings and firmware tuned for streaming writes, where a dropped frame matters more than a retried read. Mixing desktop drives into an array is the most common cause of premature recorder failure we see.
Specified by pixel density, not by megapixels
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Credentials that cannot be copied in a parking lot
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Alarms that mean something, so someone still answers them
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Protection on day one, before there is power or a fence
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Someone watching, not just something recording
Read more →Thirty days covers most operational disputes. Sixty to ninety is common where incidents surface through insurance or a customer complaint weeks later. Check your insurance policy and any shipper or client contract first — a minimum is often already specified there.
On-premise for bulk retention, cloud for the subset that matters. A recorder bolted down on site is still the cheapest way to hold ninety days of 24 cameras, but it can be stolen. Replicating alarm events and door-forced clips off-site covers the one failure mode on-premise alone does not.
It can, and it should not. Twenty-four cameras at 8 Mbps is 192 Mbps of constant traffic. Put cameras on their own VLAN with a controlled route to the recorder, and give the recorder no direct path to the internet.
OEM-imposed security requirements and process IP protection. Interior zone control and access audit trails usually outrank perimeter coverage. Cambridge is an automotive manufacturing centre, and the tier-one and tier-two suppliers clustered around it operate under customer security requirements that are frequently more demanding than anything the business would specify for itself.