In the network video surveillance system, the transmission of audio and video streams is based on the IP network. In the presence of a large number of audio and video streams, how to effectively store audio and video data and retrieve and replay video files for multiple users? Management is an important subject.
Therefore, this article discusses the storage technology of the network video surveillance system, and provides a design scheme and specific implementation of the audio and video storage server software. Supports the duplex mode of image storage and network playback. It can record multiple channels of video at the same time. It supports multiple users to retrieve and replay historical data online at the same time. The stored data can be stored in multiple ways according to the image, recording time, alarm event category, etc. Image data is retrieved.
File storage for media streamsThe typical monitoring and storage data management Solution in the industry is "DVS + Media Server + Storage System", where the media server is the core of the system and is responsible for media data stream distribution, recording, and VOD on-demand.
In this kind of streaming media server solution, the data management method is based on the file system. When all the video data passes through the media server, they are converted into standard streaming media files (a few minutes to tens of minutes of video recording). A file), and then store it. This storage method uses the characteristics of the traditional file system itself, and the system development is relatively simple, but it may reduce the efficiency of monitoring storage, which is mainly reflected in:
There is a risk of video data loss. File formation takes time. During the formation process, if there are errors in the network, front-end DVR/DVS/IPCAM failure/power failure, and the server's own software defects, it will cause the loss of the entire period of video files.
Affected by file fragmentation. A large number of file fragments will be formed during the use of the file system, and the storage space will gradually become smaller during use, and the performance will also be reduced accordingly.
Document retrieval efficiency is low. The smallest unit of historical data retrieval is a file, which is too granular and has low accuracy.
In addition to the shortcomings of the file system itself, the solution will also be affected by the capacity of the streaming media server cluster. An ordinary PC Server can carry the processing of dozens of 2Mbps media data streams. Under this kind of networking, to support a larger number of media stream processing, multiple media servers need to be formed into a cluster. However, limited by the clustering capabilities of media streaming servers, the number of media servers cannot be too many. Generally, a dozen media servers reach the limit of a cluster. Therefore, the media server cluster has become the bottleneck of the entire monitoring system, which makes the monitoring system unable to be deployed on a large scale. When building a large-scale monitoring system such as the Ping An Project, this solution will encounter big problems. A large number of media servers not only increase the cost, but the management becomes more complicated at the same time.
It can be seen that the traditional monitoring system faces two main problems in data management: ordinary file systems are not designed for monitoring storage, so it will affect the efficiency of monitoring data storage; media server clustering capabilities are limited, resulting in large monitoring systems Difficulty in scale deployment. So, is there a better data management method for monitoring storage?
In view of the data characteristics of monitoring and storage, the industry began to try some new data management methods as early as a few years ago, hoping to improve the data management efficiency of monitoring and storage, and meet the needs of monitoring large-scale applications. Among these data management methods, "block direct storage" is one of the more distinctive ones, which has become the development direction of the industry. Its innovation is mainly reflected in:
Creatively adopted the special data structure of "time index + block data", abandoned the traditional file system, and improved the management efficiency of monitoring data.
Creatively adopted the IP SAN direct storage technology based on iSCSI protocol, abandoned the traditional streaming media server, and simplified the system architecture.
Through centralized data management, the unified division and scheduling of resources is realized, and the overall management of data is realized.
Media server file storage modeIn fact, in many large-scale monitoring schemes, in order to solve the problem of the performance bottleneck of the media server, it is generally done in the form of a server farm. But it brings new problems, such as how to share load among multiple servers? After a server fails, how does the system switch data traffic to other servers? How are these servers managed? How to share a storage space? Wait, to solve these problems requires a very good cluster management system. While increasing the complexity of the system, it also requires a large budget. What's more, there is no cluster management system in the industry that can solve this problem well. problem.
Therefore, the end-to-end direct storage from the front-end equipment to the IP SAN is a good solution. In terms of storage method, the data management method of "data block direct storage" abandoned 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 recording data based on the iSCSI protocol. Write to the IP SAN storage device.
Surveillance video retrieval efficiencyIn traditional surveillance, for the file storage mode of the media stream, during the video retrieval, the corresponding file must be found first according to the camera and the retrieval time, and then the specific time point is further located, and the video is played back from that time point. The smallest unit of historical data retrieval is a file, which is too granular and has low accuracy.
The file system was originally designed for random read and write data management applications, and the retrieval efficiency is low. The retrieval efficiency of a system containing several million files is hard to imagine. Therefore, when the scale of the system is expanded, the efficiency of the traditional digital surveillance solution drops quickly.
In the "block direct storage" system, "block" storage can be understood as a custom file system that reads and writes data on the bare disk; time is used as the index of each data unit, and the index and data unit are saved On a completely independent logical storage space. The index and data of the video form an independent and complete data structure. This data structure is completely managed by itself, and is no longer managed by the operating system and files. Through the combination of time index + block data storage, the video retrieval can be retrieved based on time, and the video at any time can be quickly located, and retrieval efficiency is greatly improved. In terms of the granularity of retrieval, it is no longer limited by file size, and continuous retrieval in seconds can be achieved.
H3C Innovative Storage Model—"iSCSI Block Direct Storage"As one of the leading manufacturers in the IP field, H3C also has a long-term accumulation of technology and products in the fields of IP networking, IP video, and IP storage. After entering the field of IP surveillance, H3C merged these technologies and was the first to introduce the storage method of iSCSI block storage into the surveillance, thus effectively solving the problems of storage performance, reliability and retrieval efficiency introduced by the media server.
On the basis of both "block data" and "direct storage" technologies, through the unified division and scheduling of global resources, the global management of data is realized. In a large surveillance system, there may be thousands of cameras and massive storage space.
How to manage the correspondence between these cameras and storage devices is a very complex problem. In the "block direct storage" 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, all cameras and storage resources are managed by it. When the camera needs storage resources, it will apply to the DM uniformly. The DM will select a suitable storage resource from the storage space and allocate it to the camera, so that the camera can establish a read-write relationship with this storage resource.
After the IP SAN device completes the storage of a certain camera media data block, it automatically generates a block index value according to the IP address of the monitoring point and the start and end time of writing the media data. Communicate between DM and IP SAN, obtain the latest video storage information, and retrieve all surveillance images through DM.
Of course, this storage method inevitably puts forward higher requirements on the technical accumulation and strength of surveillance manufacturers. For example, the encoder is required to support dual-streaming, the real-time surveillance video stream and the stored video stream can be encoded independently, and the encoder supports the iSCSI protocol.
Dual stream is the basic requirement of all current high-end encoders, and many manufacturers have implemented it. The encoder supports iSCSI, which requires monitoring vendors to have professional storage technology accumulation. For most current monitoring vendors, there is a certain technical threshold. Fortunately, we see that more and more surveillance vendors recognize the importance of storage for a surveillance solution and begin to accumulate technologies in this area.
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