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Calculating storage needs

The emergence of network video systems calls for increased use of hard disk storage. This gives rise to a number of questions, ranging from how much hard disk is needed to how to build fail-safe hard disk storage.

Required hard disk space

Factors to consider when calculating storage needs:

* Number of cameras.

* Number of hours per day the camera will be recording.

* How long the data must be stored.

* Motion detection (Event) only or constant recording.

* Other parameters such as frame rate, compression, image quality and complexity.

Note that the calculation examples below are examples only and do not take into consideration any overhead or other technical issue that may result in a higher file size than mentioned below.

The calculation examples below do not consider storage space for the operating system or video management software.

JPEG or Motion JPEG

For JPEG/Motion JPEG where single files are received, storage requirements vary by changing the frame rate, resolution and compression: Cameras 1, 2 and 3 in the table below have different storage requirements according to their fps (frames per second) and resolution settings.

Total for the three cameras and 30 days of storage = 1002 GB

Calculation:

Image size x frames per second x 3600s = KB per hour/1,000 = MB per hour.

MB per hour x hours of operation per day/1000 = GB per day.

GB per day x requested period of storage = Storage need.

MPEG-4

In MPEG-4, the images are received in a continuous data stream, ie, not individual files. It is the bit rate - measuring the amount of video data transmitted - that determines the corresponding storage requirements. The bit rate is a result of specific frame rate, resolution and compression, as well as the level of motion in the scene.

Total for the three cameras and 30 days of storage = 204 GB

Calculation:

Bit rate/8 (bits in a byte) x 3600s = KB per hour/1,000 = MB per hour

MB per hour x hours of operation per day/1000 = GB per day

GB per day x requested period of storage = Storage need

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