Storage sizing: from measured bitrate to usable capacity
Keep units, recording duration and disk overhead explicit.
Updated
Principle and limits
Use average measured bitrate for volume and peak bitrate for throughput checks. One continuous 1 Mb/s stream produces 10.8 decimal GB per day: 1,000,000 ×86,400 /8 bytes. For identical streams, TB = cameras × Mb/s × days ×0.0108. Add audio separately if it is not included in the measurement. Decimal TB and binary TiB are different units.
Worked example
Sixteen cameras at 4 Mb/s for 30 days require 20.736 TB of video payload. A chosen 20% planning reserve gives 24.8832 TB; 20% is a project assumption, not an industry guarantee. Required installed disks depend on RAID, spares, formatting and recorder limits. RAID improves availability for specified failures; it is not a backup against deletion or every failure.
Installation and acceptance
Measure representative busy and quiet periods, including night noise. Event recording needs measured duty cycle plus pre/post-event buffers; do not assume activity occupies ten percent of the day. After commissioning, inspect actual daily growth and oldest retrievable footage. Repeat after stream changes and test export while recording continues.
Derive the calculation and keep units visible
For a constant average bitrate R in Mb/s and recording time d in days, decimal storage is R × 10⁶ × 86400 × d / 8 bytes. Divide by 10⁹ for GB or 10¹² for TB. Therefore 1 Mb/s continuously consumes 10.8 GB per day, and 16 × 4 Mb/s × 30 days produces 20.736 TB of video payload. If an operating system reports TiB, divide bytes by 2⁴⁰ instead; 1 TB and 1 TiB are not interchangeable.
For different camera rates, sum each rate multiplied by its own recording duration. Add recorded audio explicitly. Motion-only recording cannot be sized reliably by an arbitrary percentage: use measured event occupancy and include pre-event and post-event recording. Busy scenes can approach continuous recording.
Reserve is a design assumption, not free capacity
Adding 20% to a calculated payload means payload × 1.20. Keeping 20% of the installed usable capacity free means payload / 0.80. For 20.736 TB those are 24.8832 TB and 25.92 TB respectively. State which rule you use: they are different. Neither is a mandatory universal margin.
Obtain usable capacity after RAID, hot spares, filesystem and recorder allocation. A nominal drive total does not show retained recording space. RAID may improve continuity under specified failures but is not an independent backup or evidence archive. Test the earliest retrievable recording after a full retention cycle and inspect gaps during peak activity and recovery. Any shorter commissioning test must be labeled as a projection.
Scope of the reference
RFC 8836 discusses transport congestion and variable media rates. It does not prescribe CCTV disk capacity or certify a recorder. Storage examples above are dimensional calculations with explicitly chosen recording assumptions.