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As video surveillance images become more and more clear, storage time becomes longer and longer, and storage reliability requirements become higher and higher, video data storage gradually shifts from digital video recorder (DVR) to professional IPSAN professional storage devices, especially In the monitoring of the park is more obvious. In the park monitoring, not only the security monitoring of the park but also the production business must be monitored. In the traditional monitoring, the media server file storage mode has not been able to solve the needs of the new storage services, such as the 'dumbbell' effect of the media server, the rapid retrieval of production monitoring emergency, and the problem of historical video playback. Solving these problems requires re-selecting the storage mode in monitoring and breaking the file storage mode of media streams in traditional monitoring.
The traditional monitoring of media stream file storage uses streaming data to form a file for storage. All historical image playback is through the playback of stored video files. During file formation, management personnel cannot read the file. For example, in many monitoring applications of the 'DVR/DVS+ streaming media server' approach, the monitoring image is stored in a manner that forms a video file every half hour. This means that Historical images less than half an hour before the current time cannot be called.
In the event of an emergency, people want to be able to see historical images as soon as possible, and even require that they can be played back at any time. This requires that the time interval for data streams to form files is as short as possible, but this will cause huge performance pressure on the system. If a video file is formed in 5 minutes, each monitoring point will generate nearly 300 files a day. If the historical image of each monitoring point is to be stored for 30 days, it means that each monitoring point needs to generate nearly 9000 files. For a large-scale monitoring system of 1000 roads, 9 million files will need to be processed, and the system must be overwhelmed.
In response, the industry began to try new data management methods as early as a few years ago, hoping to improve the data management efficiency of monitoring storage and meet the needs of monitoring large-scale applications. Among them, 'block storage' is a more characteristic way. This method adopts a special data structure of 'time index + block data', abandoning the traditional file system, and improving the management efficiency of monitoring data.
Performance bottleneck and reliability of the media server In the traditional mode, when it is necessary to achieve centralized storage or support multiple people to view a monitoring point at the same time, the media server is used for transferring or copying. In this way, the media server needs to convert the media stream into files for storage. The front-end media stream data is transferred to the back-end storage device via the media server. The processing performance and bandwidth of the server can easily become the performance bottleneck. The performance of the entire system is distributed into a dumbbell shape, which also increases the failure points. The failure of the media server affects the entire system's monitoring and storage services.
Media server file storage mode In fact, in many large-scale monitoring solutions, in order to solve the problem of media server performance bottleneck, the general use of server groups to complete. But this will create new problems, such as how to load balance among multiple servers. After a server failure, how does the system switch data traffic to other servers? How do these servers manage? How to share a storage space? Solving these problems requires a very good cluster management system, which increases the complexity of the system and requires a large budget. Unfortunately, there is not yet a cluster management system in the industry that can solve this problem well.
Therefore, the end-to-end direct storage of the front-end device to the IP SAN is a good solution. In the storage mode, the data management method of “direct storage of data blocks†abandons the media server. On the basis of the IP network, the iSCSI module is integrated in the encoding device so that the encoding device can end-to-end record data based on the iSCSI protocol. Write to the IP SAN storage device.
The search efficiency of surveillance video is monitored in the system. The file storage mode of the media stream must first find the corresponding file according to the camera and retrieval time during the video retrieval, and then further locate the specific time point and play back the video from the time point. The smallest unit of historical data retrieval is the file, with too large a granularity and low accuracy.
The file system is originally designed for data management applications that are read and written at random, and the retrieval efficiency is low. The retrieval efficiency of a system with several million files is hard to imagine. Therefore, when the scale of the system is expanded, the efficiency of the traditional digital monitoring scheme drops rapidly.
In a 'block-by-block' system, 'block' storage can be understood as a custom file system where data is read and written on a bare disk; time is used as an index for each data unit, and index and data units are saved In a completely independent logical storage space. The index and data of the video form an independent and complete data structure. This data structure is entirely managed by itself and is no longer managed by the operating system and files. With the combination of time index + block data storage, retrieval can be performed based on time in video retrieval, and the video can be quickly located to an arbitrary time, and the retrieval efficiency is greatly improved. The granularity of the search is no longer limited by the size of the file, and continuous search in seconds can be achieved.
H3C innovative storage mode - 'direct storage of iSCSI blocks'
As one of the leading vendors in the IP field, H3C has long-term technology and product accumulation in IP networks, IP video, and IP storage. After entering the IP surveillance field, the H3C converged these technologies and introduced the storage method of iSCSI block storage into monitoring for the first time, which effectively solved the problems of storage performance, reliability, and retrieval efficiency introduced by the media server.
On the basis of both the 'block data' and 'direct memory' technologies, global data management is achieved through global resource division and scheduling. In a large-scale surveillance system, there may be tens of thousands of cameras and a large amount of storage space. How to manage the correspondence between these cameras and storage devices is a very complicated problem. In the 'direct block' video surveillance system, H3C introduced a data management server unit (DM) to achieve unified management of storage resources.
DM is a dedicated data management device, and all camera and storage resources are managed by it. When the camera needs storage resources, it will apply to the DM in a unified manner. The DM will allocate appropriate storage resources from the storage space to the camera, so that the camera will establish a read-write relationship with the storage resource of this block.
After the IP SAN device completes the storage of a certain camera media data block, a block index value is automatically generated according to the IP address of the monitoring point and the start and end times of the written media data. Communication between the DM and the IP SAN is performed to obtain the latest video storage information, and retrieval of all the monitoring images is performed by the DM.
Of course, this storage method will inevitably impose higher requirements on the technology accumulation and strength of the monitoring vendors. For example, the encoder is required to support dual stream, real-time monitoring of the video stream and storage of the video stream can be independently encoded, and the encoder supports the iSCSI protocol. Dual-stream is the basic requirement of all high-end encoders nowadays, and there are many vendors that implement it. Encoder support for iSCSI requires the monitoring vendors to have professional accumulation of storage technologies. For most current monitoring vendors, there are certain technical thresholds. Fortunately, we see that more and more monitoring vendors recognize the importance of storage for a monitoring program and begin to accumulate technology in this area.
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