Your 4K camera records 86 GB/day. Your HDD fills in 11 days. And the vendor sold you “30-day retention” without doing the math with you.

The formula: 1 Mbps × 10.8 = GB/day (universal constant).

( Derives from: 1 Mbps × 1/8 bytes/bit × 86,400 sec/day ÷ 1,000 = 10.8 GB/day )

For 10 4K H.265 cameras @ 8 Mbps each, over 30 days:

→ 8 Mbps × 10.8 × 10 cameras × 30 days = 25,920 GB ≈ 26 TB raw

But nobody buys “26 TB”. You buy 40 TB. Why? 40-60% overhead for RAID 5/6, file system, and 80% fill headroom. If your integrator quotes you 26 TB, you won’t make it 30 days.

What nobody tells you:

  1. The “30-day retention” offered in marketing usually assumes motion-triggered recording, not continuous. If you record 24/7, divide that number by 3-4.
  2. RAID 6 is your friend with disks >10 TB. URE risk during rebuild rises significantly with larger disks. RAID 5 is for tight budgets, RAID 6 for production.
  3. Smart codecs (Zipstream, H.265+) aren’t magic: they cut bitrate when there’s no motion, but they DON’T recover storage you’ve already burned.

P.D. How many TB do you have provisioned today vs how many you’d need with continuous 24/7 recording × 30 days × your 10 cameras? If the gap is >2x, today’s a good day to recalculate before the disk fills.

📰 Source: own calculation based on bitrate × 10.8 GB/day + RAID overhead industry standard 40-60%.