Considerations For Bandwidth and Storage Space

The network bandwidth and storage space required are important factors in the design of a video surveillance system. Factors include the number of cameras, the image resolution used, the type and proportion of compression, frame rates, and scene complexity. This chapter presents some design guidelines for a system as well as information about storage solutions and various system configurations.

Bandwidth and storage space calculations

Network video products use network bandwidth and storage space according to your configuration.As already mentioned, this depends on the following factors:

  • Number of cameras
  • Recording method (continuous or by event)
  • Number of hours per day the camera will record
  • Frames per second
  • Image Resolution
  • Video compression type: Motion JPEG, MPEG-4, H.264
  • Scene: image complexity (eg white wall or a forest), lighting conditions and amount of movement (office environment or crowded train stations)
  • Expected time of data storage

Required bandwidth

In a small surveillance system with 8 to 10 cameras, a basic 100 megabit (Mbit) network switch can be used without the need to think about bandwidth limitations. Most companies can implement such a surveillance system using the network they already have.

When implementing 10 or more cameras, the network load can be calculated by some general rules:

  • A camera configured to generate high quality images at high frame rate will use approximately 2 to 3 Mbit / s of the available network bandwidth.
  • Between 12 and 15 cameras, consider using a high-speed backbone (gigabit) switch.If a high-speed switch is used, the server where the video management software is installed must have a gigabit network adapter installed.

Among the technologies that allow managing bandwidth consumption are VLANs in a switched network, Quality of Service, and event-driven recordings.

Calculation of required storage space

As already mentioned, the type of video compression used is one of the factors that affect the storage space required.The H.264 compression format is by far the most efficient video compression technique available today.Without compromising image quality, an H.264 encoder can reduce the size of a digital video file by more than 80% compared to the Motion JPEG format, and up to 50% more than the MPEG-4 standard (Part 2 ).This means that you will need much less network bandwidth and storage space for an H.264 video file.

The tables below show examples of storage space calculations for all three compression formats.Because several variables affect average bitrate levels, calculations are not so straightforward for H.264 and MPEG-4 formats.With Motion JPEG, the formula is clear because this format consists of a single file for each image.The storage space required for Motion JPEG files varies depending on the frame rate, resolution, and compression level.

Calculation for H.264 format

Approximate speed / 8 (bits in one byte) x 3600s = KB per hour / 1000 = MB per hour
MB per hour x hours of daily operation / 1000 = GB per day
GB per day x expected storage period = required storage space

Calculation for MPEG-4 format

Approximate speed / 8 (bits in one byte) x 3600s = KB per hour / 1000 = MB per hour
MB per hour x hours of daily operation / 1000 = GB per day
GB per day x expected storage period = required storage space
Note: The formula does not take into account the amount of movement, which is an important factor that can influence the storage space required.

Calculation for Motion JPEG format

Image size x frames per second x 3600s = Kilobyte (KB) per hour / 1000 = Megabyte (MB) per hour
MB per hour x hours of daily operation / 1000 = Gigabyte (GB) per day
GB per day x expected storage period = required storage space

A useful tool for calculating the required bandwidth and storage space is the AXIS Design Tool .

Server Storage

Depending on the central processing unit (CPU), the network card, and the internal RAM (Random Access Memory) of a server PC, it can handle a certain number of cameras, frames per second, and image size.Most PCs can contain between two and four hard drives, and each disk can hold up to approximately 300 gigabytes (GB).In a small or medium-sized installation, the PC on which the video management software is installed is also used for video recording.This storage method is called “direct connection.”

With AXIS Camera Station video management software, for example, a single hard drive is enough to store six- to eight-camera recordings.With more than 12 or 15 cameras, at least two hard drives must be used to divide the load.For 50 cameras or more, it is recommended to use a second server.

NAS and SAN

When the amount of data stored and the need for management exceeds the limits of a direct-attached storage, a network-attached storage (NAS) or a storage area network (SAN) will increase storage space, flexibility, and capacity recovery.

The NAS is a single storage device directly connected to a LAN, offering shared storage to all network clients. A NAS device is simple to install and easy to administer, providing an economical storage solution. However, it offers limited speed for receiving data because it has only one network connection, and this can become a problem in high-speed systems. SANs are dedicated high-speed networks for storage, typically connected to one or more servers through fiber. Users can access any of the SAN storage devices through the servers, and the storage space can reach hundreds of terabytes. Centralized storage reduces administration and provides a flexible and speed storage system for use in multi-server environments. Fiber Channel technology is typically used to transfer data at 4 gigabits per second and allow the storage of large amounts of data with a high level of redundancy.

Redundant storage

SAN systems incorporate redundancy into the storage device.Redundancy in a storage system allows videos, or any other type of data, to be recorded simultaneously in more than one location.This creates a backup to recover videos if a part of the storage system is unreadable.There are several options for delivering this layer of additional storage on an IP Surveillance system, including a Redundant Array of Independent Disks (RAID), data replication, clustering of servers, and multiple video recipients.

RAID.RAID is a standard, commercially available hard disk array method so that the operating system refers to it as a single large hard disk.A RAID configuration spreads the data across multiple hard drives with sufficient redundancy so that data can be recovered in the event of a disk failure.There are different levels of RAID, from virtually no redundancy to an entirely mirrored solution in which there is no interruption or loss of data in the event of a hard disk failure.

Duplication of data.This is a common feature of many network operating systems.File servers on a network are configured to replicate data to each other, creating a backup if a server fails.

Clustering of servers.A common method of server collation is to have two servers work with the same storage device, such as a RAID system.When one server fails, the other server configured identically will assume its function.These servers may even have the same IP address, each failover completely imperceptibly for users.

Multiple video recipients.A common method for securing disaster recovery and remote network video storage is to simultaneously send the video to two different servers in separate locations.These servers can be RAID-equipped, operate in clusters, or duplicate your data with even further servers.This is an especially useful approach when surveillance systems are in hazardous or hard-to-reach areas, such as in mass transit facilities or industrial facilities.

System Settings

Small system (1 to 30 cameras)

A small system typically consists of a server with a surveillance application installed to record the video images on a local hard drive.The video is viewed and managed through the same server.Although most of the visualization and management is performed on the server, a client (local or remote) can be connected for the same purpose.

Medium-sized system (25 to 100 cameras)

A typical midrange installation has a server with additional storage attached to it.Typically, storage is configured with a RAID to increase speed and reliability.Normally, the video is displayed and managed through a client, not the recording server itself.

Large centralized system (50 to more than 1000 cameras)

A large installation requires high speed and reliability to manage the large amount of data and the large bandwidth.This requires multiple servers with dedicated tasks.A master server controls the system and decides what type of video will be stored on that storage server.Because there are dedicated storage servers, you can perform load balancing.In this configuration, you can also extend the system by adding more storage servers when needed, and perform maintenance tasks without disabling the entire system.

Large distributed system (25 to more than 1000 cameras)

When multiple locations require monitoring with centralized management, distributed recording systems can be used.Each location records and stores video from local cameras.The master controller can view and manage the recordings of each location.

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