Introduction
NVR – the Network Video Recorder (NVR) is an extension of the DVR where the storage and encoding are separated. Rather than connecting analogue video directly to the recorder where it is compressed before being recorded, the video is compressed by an encoder or IP camera and transmitted over the network to the NVR where it is recorded to hard-disk. Some of the latest DVRs can now also accept video feeds from IP cameras, blurring the lines of distinction between a DVR and an NVR.
Digital video is generally stored on hard-disks by the NVR or NVMS. Depending on the size of the system these may be internal hard-disks within the NVR chassis, or they may be in a separate RAID (Redundant Array of Independent Disks) array. On larger systems, the storage may take the form of a Storage Area Network (SAN) consisting of several SAN storage units connected to a high-speed fibre-channel or iSCSI network. A typical 42-disk SAN unit populated with 2TB SATA disks has a physical capacity of 84TB. However, when this is arranged as four separate RAID5 sets with two hot-spare drives then the usable capacity is reduced to 72TB.
