Ten to 15 years ago, tape was the preferred storage medium for recorded video. At most, it held eight hours of video from a single camera at full frame rate. Then DVRs came along, which eliminated the cumbersome process of changing tapes, but you were limited to the storage capacity delivered by the manufacturer.
Only when IP-based network video hit the market did the digital revolution for video storage really begin to take off. Companies could use common off the shelf (COTS) storage systems, enabling them to incorporate rapid advancements in storage capacity and redundancy, at ever-lower costs. This was especially beneficial in video surveillance applications where archiving consumes a large amount of storage. But this is just the beginning of the storage revolution.
Exponentially Increasing Capacity
Today, you can buy 1.5 terabyte drives for as little as $129, which amounts to less than a dime per gigabyte of storage. A camera using H.264 compression and VGA resolution typically consumes 10 GB per day when storing full frame rate video, which comes to less than $2 per day in hard disk costs. That means a 1.5 TB drive could store more than 100 days of full-frame-rate video.
By contrast, the first laptop I bought in 1992 had a 25 MB drive that could only have stored one minute of full-frame-rate video if I had used H.264 compression. But back then, H.264 was not available, so I would have had to use JPEG, which meant I could have only stored 10 seconds of video on the drive. Since then, capacity has literally doubled every year, which means that compared to 20 years ago, today's regular hard drive can now store one million times more video.
More Efficient On-Board Storage Options
One of the more interesting trends in storage today are SSD, or solid state drives, which have already revolutionized the consumer electronics market. Think how fast and inexpensive memory is today for digital still and video cameras. Even laptops are starting to use SSD - also known as flash drives - to increase reliability, reduce power needs, decrease weight and improve processing speed. One day, we might very well see flash drives replace spinning magnetic discs altogether - at least in laptops.
In addition to increasing memory, the footprint of high-capacity memory card technology continues to shrink. The most common format is the SD-card (Secure Digital), which at less than two square inches, houses up to 32GB for about $50. Its small size means it can be housed inside the network camera, enabling the camera to reliably store a few days worth of full-frame-rate recordings on board.
This opens up new possibilities for maintaining physical security in locations unsuitable for housing servers to manage the video recordings. In fact, the recently released SDXC format (XC for eXtented Capacity) will eventually provide capacities up to 2TB per card, allowing months or even years of video storage inside of the camera.
More Scalable Storage Architecture
The other half of the storage revolution has been advances in storage architecture to effectively scale video surveillance systems from one to thousands of cameras. Huge storage capacities and lightning-fast data communications provide companies with endless variations in storage solutions. Three basic storage architectures can serve as the foundation for a video surveillance system:
Server-based: This is the traditional system, where a server hosts the video management application and the storage connects directly to the server. The most common server system contains two or more disks, enabling RAID redundancy in the case of a disk failure. This configuration is typically used for 10- to 100-camera systems because it easily expands into a larger system by multiplying the number of servers and connecting groups of cameras to each server. A more advanced architecture would entail connecting the server to a Storage Area Network (SAN), which would encompass an array of storage shared by multiple servers.