Surveillance storage is a constant, sequential write from many cameras with long retention — so the best RAID is capacity-led, resilient and built on surveillance-rated drives. Size your retention in the RAID calculator.
What CCTV/NVR storage demands
Unlike most workloads, surveillance writes continuously — every camera streams 24/7, so the array sees a steady, mostly-sequential write load and occasional reads (review/export). The dominant requirements are capacity (retention × cameras × bitrate), sustained write reliability, and surviving a drive failure without losing footage.
That points to large nearline or surveillance-rated HDDs in a dual-parity array: RAID 6 (or RAID 60 for very large NVRs), or RAIDZ2 on a ZFS-based recorder. Single parity is risky on the big drives surveillance uses.
Use surveillance-rated drives
Standard desktop drives aren't built for the constant write workload of CCTV. Surveillance drives (WD Purple, Seagate SkyHawk and similar) are rated for 24/7 writes, many simultaneous camera streams, and higher annual workload — and they tune firmware for streaming rather than bursty desktop I/O. For larger systems, enterprise nearline drives work well too.
Match drive count and capacity to your retention target; the calculator turns drives × capacity × RAID level into usable TB so you can check it covers your required days of footage.
Sizing retention
Estimate usable capacity needed as: cameras × bitrate × hours-per-day × retention-days (then convert bits to bytes and add ~20% headroom). Compare that to the array's usable capacity in the calculator. Remember parity and (for ZFS) slop/padding reduce raw to usable — the calculator accounts for it.
RAID keeps the recorder running through a disk failure, but for evidential footage consider a second copy or off-site archive too — RAID is not a backup.