Compact desktop NVRs hold 1-2 drives — typically capping around 16TB usable. Mid-size rack-mount NVRs hold 4-8 drives, often 32-64TB usable in RAID 5/6. Enterprise NVRs and dedicated storage servers scale to 16+ drives with hot-swap and JBOD expansion. Match drive count to your retention math; running out of drive bays mid-project means a recorder replacement, not just a drive add.

Surveillance-grade drives (WD Purple, Seagate SkyHawk) are correct for most NVRs — they're tuned for many concurrent write streams from cameras with low read count. Enterprise drives (WD Gold, Seagate IronWolf Pro, Exos) are appropriate for high-channel-count systems with many concurrent investigator clients reading recorded video. Avoid desktop drives entirely; they're rated for 8x5 light duty and fail quickly in 24/7 NVR loads.

An NVR records exclusively from IP cameras over Ethernet. A hybrid (or tribrid) recorder accepts both IP cameras and legacy analog/HD-over-coax cameras on dedicated BNC inputs, useful for migrations where you can't replace coax runs immediately. Hybrid units cost more per channel and add complexity; if you're starting fresh or fully replacing analog, a pure NVR is simpler and almost always cheaper per usable channel.

Most rack NVRs and storage servers accept storage expansion via empty drive bays, eSATA/SAS JBOD shelves, or iSCSI targets. Desktop NVRs with only 1-2 bays generally do not. Before buying, check the recorder's supported expansion architecture and the maximum raw and usable capacity — many sub-$2,000 NVRs cap below the 24TB threshold most projects need within three years.

For a few cameras and one or two simultaneous operators, the NVR's built-in client interface is enough. For 32+ cameras, multiple investigator seats, video walls, or wall-of-monitors operations, a dedicated workstation (or thin client) running the VMS client is standard. The workstation needs adequate GPU decode capacity for the simultaneous stream count — H.265 decode acceleration is essential at scale.