In recent years, the market share of analog video surveillance systems has been shrinking. As one would expect, IP video surveillance is gaining popularity. Indeed, IP video surveillance solves the cumbersome problem of traditional surveillance wiring, but it also brings new problems.
Analog cameras have reached the highest level of 650 lines, but for IP cameras, the current technical level has already exceeded the limit of megapixels, and cameras with two million, five million, or even tens of millions of pixels are no longer. "Things are rare", and the improvement of the quality of the image collected by the front end also puts forward requirements on the back-end monitoring storage device.
Generally speaking, the current video surveillance mainly adopts the following ways to store:
DVR storage
This is currently the most common storage mode. The codec device is directly connected to the hard disk. Currently, it can bring up to 8 hard disks. However, due to the limitation of the performance of the coding and decoding equipment, the sequential writing mode of the hard disk is generally adopted, and RAID redundancy technology is not applied to achieve data protection. With the continuous increase of hard disk capacity, the probability of single-chip hard disk failure leading to the loss of key data is increasing synchronously, and the limitations of DVR performance also affect the sharing and analysis of image data.
NVR storage
In the video surveillance system, NVR is an ideal upgrade product for analog video recorders and hard disk video recorders. It is a stand-alone independent operation device that realizes the exemption of window operating system and computer cooperation based on the original DVR. Since NVR adopts highly integrated chip technology, it has advanced digital video recording, storage and playback functions, no need to replace and store video tapes, no computer cooperation and daily maintenance, so it can achieve high resolution (up to Full-D1 resolution Rate), high-quality real-time monitoring, and easy to use. Simply put, the NVR system digitizes traditional video, audio and control signals, and transmits them on the network in the form of IP packets through the network interface on the NVR device. On the basis of DVR, the system is networked.
Encoder external storage device directly connected storage
Connected through the external storage interface of the codec, it is mainly expanded using storage protocols such as SATA, USB, iSCSI and NAS. In this way, the capacity of the codec can be further expanded, which is suitable for small and medium-scale deployments. The reliability of the surveillance video data is guaranteed by RAID technology. Among them, the direct connection mode adopted by the SATA / USB mode cannot be shared and has low expansion capability. The IP network (iSCSI and NAS) has better expansion and sharing capabilities. Due to the direct writing of data, this step of server transfer is reduced, and the user's investment is saved while the performance is improved. However, when data is forwarded and retrieved in this way, it is easy to have a big bottleneck in the forwarding link. At present, direct write usually adopts storage methods such as NAS. Due to NAS's file protocol and other reasons, the efficiency of multiple nodes writing data concurrently is not high.
Centralized storage management
The server connects to the front-end codec, downloads the data through the streaming media protocol, and then stores it on the storage device. Servers and storage devices can be connected via SAS, iSCSI, NAS, FC protocols. The centralized storage method is suitable for the deployment of large and medium-sized platforms. Among the centralized storage methods, the IP connection mode (iSCSI) and the FC connection mode have good scalability and manageability, and are currently one of the more adopted methods. In terms of actual deployment and effects, FC storage is more suitable in a monitoring environment with more nodes due to its powerful performance and data processing capabilities, while IP storage can be more suitable for small and medium-sized applications due to performance and scalability limitations. High cost performance.
Unlike other IT systems, video surveillance systems are relatively demanding in terms of large capacity and cost. It is hoped that the system can be expanded to achieve tens of thousands of roads and hundreds of thousands of roads of monitoring, but the capital of hundreds of millions of dollars is also a sensitive topic. Behind the high cost, relevant data shows that when using traditional DVR and NVR solutions, storage equipment accounts for 15% to 30% of the cost of the entire video surveillance system; and for digital network HD video surveillance systems, storage equipment is The cost of the entire system rose to 50% to 70%. In other words, controlling storage costs has become one of the deciding factors in reducing the total cost of video surveillance systems. Therefore, while ensuring the security of the system, choosing a large-capacity and low-cost IP storage system has become an important task for us to build a video surveillance system.
Select the appropriate storage device according to the system configuration
We know that the size of the storage device's capacity is not only related to the number of cameras, but also related to the video format, bit rate, and storage days. The storage system capacity is calculated as follows:
Assume that the format of the video is D1 and the code rate is 2Mb / s. The daily storage capacity of single channel video is: 1 channel * (2Mb / s * 3600s) / 8bit * 24 hours = 21GB. The monthly storage capacity of single channel video is: 1 channel * (2Mb / s * 3600s) / 8bit * 24 hours * 30 days = 648GB. We can choose according to the actual situation according to the number of cameras, bit rate and storage time.
Distributed PK centralized
For network video surveillance systems, the storage method is often faced with two methods, whether to choose distributed storage or centralized storage? Let us first look at the difference between the two:
Advantages and Disadvantages of Centralized Storage Centralized physical media deployment; uploading video streams to the center has high requirements for the computer room environment, large room requirements, and load-bearing and air conditioning.
Advantages and disadvantages of centralized management The physical media is distributed to different geographical locations; the video stream is uploaded nearby, and there is no requirement for the backbone network bandwidth; multiple sets of low-end small-capacity storage equipment can be deployed for deployment, and the equipment price and maintenance cost are low; The small-capacity equipment is distributed and deployed, which has low requirements for the equipment room environment.
For a monitoring system such as a safe city, how is the monitoring data stored? Are each area centralized? How is it centralized? Generally speaking, the smaller the city, the better the network conditions and the easier it is to achieve centralized storage; otherwise, the more distributed Storage, and for systems in need, the video surveillance system can be concentrated in each area and then converged to a general center, such as an emergency command center.
Purchase considerations
Unlike other storage systems, the video surveillance storage system has its own unique characteristics: access to storage devices in the form of streaming media, multiple channels of video are simultaneously written to the same storage for a long time, and real-time multiple channels of video access the same file The video access bandwidth is constant, and the bandwidth stability requirement is high, which is an average of 1/25 second. The video access time is long, the capacity requirement is huge, and the storage expansion performance is high. Video storage has no special requirements for the storage environment. The data of the conventional monitoring system is basically temporary, and can be deleted after the online storage time (generally 30 days). The backup of the monitoring system often only needs to meet one month.
In other words, the video surveillance system is first a video application system, and the storage device must be able to provide stable bandwidth output to meet the requirements of long-term video reading and writing. Second, the video surveillance system must meet the real-time data writing of a large number of cameras, and To meet the video playback requirements of a large number of monitoring ends, it is also necessary to consider that the storage system can provide sufficient IOPS performance. Because the video surveillance system covers a wide area, covering the entire city and even requiring the whole country, the storage device must also consider whether it can be physically dispersed, but can be unified in management and monitoring.
Therefore, when we choose to monitor storage devices, we don't necessarily choose the one with the largest bandwidth, but the one with the smallest bandwidth fluctuation and the most stable curve. Since the video surveillance system requires 24 hours a day to run for a long time, it is best to use a storage device with a controller architecture. Do not choose a PC-based storage device. Choose a device with a capacity that can be expanded.
In addition, in the case of more than 100TB capacity, the price of FC-sata equipment is not necessarily more expensive than ISCSI equipment. FC supports a large number of disks, and ISCSI devices generally support a small number. Assuming that the capacity requirement is 500TB, FC-sata only needs one set, and ISCSI devices need a lot, only the cost of the ISCSI device controller department It's a big piece.
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