![]() ![]() Distributed Storage ArchitecturesĪ typical example of such a system would be a rail network that could have 200 cameras located across 25 stations with on average eight cameras per station, with some stations only having four cameras. In reality the typical casino uses between 5 cameras, so this approach is an important factor in keeping down costs. Leading NVR vendors can run their software under applications such as VMware (see panel ‘Virtual servers’) allowing ten virtual servers to be configured on one physical server, considerably reducing equipment costs. This is still a lot of hardware, but because the CPU utilisation is low, virtual servers can be deployed. Using the worked example above with a 100 camera system, one option would be to use ten NVR servers each fitted with an 18 Terabyte disk array, assuming the system has the best compression technology available. In this situation all of the video could be recorded on one server, however, this would almost certainly be storage limited, not CPU limited. The NVRs would be located in one central IT facility, with a central network switch. Centralised Storage ArchitecturesĪ typical example of such as system would be a Casino, where a high density of cameras are located in one building. The storage architecture for CCTV systems can be categorised as either centralised or distributed. Therefore, in a large system with a 90 day recording requirement, the limitation on the server is its storage, not its processing power. ![]() The best NVR server software on the market has such a low CPU loading that 200 camera streams can be recorded on the lowest specification server PC. Software which can minimise this processing will be able to handle many more camera streams per NVR. There can be a considerable difference in this overhead between different vendors of NVR software. The processing overhead for writing and reading the video streams to disk is therefore an important factor in the overall performance of the NVR. the rate of writing data to the disk is constantly high, not in bursts as with typical IT applications. The amount of data coming from the NVR to the users is very low and periodic. The amount of data coming from the cameras to the NVRs is huge and continuous. When it comes to storage, CCTV systems are very different to IT systems. The difference between an average compression and the best is 180 Terabytes of extra storage and that’s just for a relatively small system of 100 cameras. However, assume a system with 100 cameras and the storage becomes: This doesn’t at first seem unmanageable since hard disk storage is inexpensive and 750 Gigabyte disks are readily available. The amount of digital data generated by a single camera: The following worked example demonstrates the storage requirements for a typical system, comparing equipment that has an average compression with the very best that is available. The way in which video is compressed can make a significant difference to the storage requirements. So when comparing systems the main variable is the compression technology, as all other factors are constant. The factors that affect how much disc storage is required are video resolution, frame-rate, number of cameras and the quality of the compression technology deployed. Similarly, the security of the stored data is important so that individual disk and equipment failures do not result in data loss. ![]() With potentially large amounts of data being stored, the technology behind the compression employed and the architecture of the storage solution are critical to ensure these extended recording times can be accommodated. The storage element of a large IP-CCTV system can therefore dominate the overall cost of the system, both up-front costs and lifecycle costs as hard drives will often need to be replaced over the life of the project. This is compounded by users wanting to store video at the highest quality and maximum frame rate, particularly where CCTV footage is required for evidential purposes. In large systems this can create a significant storage requirement. Many organisations now require that CCTV video images are recorded and archived continuously from all cameras for 90 days or more. ![]()
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