While NAS recording currently has a strong communication link and automatic handshake with hosting systems today, be forewarned that activating an SD card failover option may require custom configuration by an integrator. As edge recording continues to improve, expect to see advanced filtering and analytic options in the not-too-distant future.
Choosing the Right Amount of Local Storage
Whether you opt for a NAS device or edge-recording, the amount of storage needed will entirely depend or the application and company’s security needs. If you plan to use the local storage strictly as a redundant safety net for network failures, then less is more; however, a NAS offers an attractive bonus: dual-streaming. This gives you the option of sending high-quality video to the local device for forensic evidence while saving on bandwidth by streaming lower-quality video to the cloud.
While 2TB NAS models start around $250, you could scale up to 12TB models for around $800 today. By the same token, SD memory cards come in a wide range of storage capacities and prices, which a quick Google search will prove. Basic SD cards range from 64MB to 4GB. SDHC (high capacity) cards offer more storage — from 2GB to 32GB. SDXC cards — the newest SD Association standard — start at 64GB and can go as high as 2TB, though the upper limit cards may take years to reach the market.
Obviously there are plenty of data size options to choose from — albeit NAS or SD — so your decision depends on a number of factors:
1. Which device/card your hosted surveillance system supports;
2. Which compression standard you use (H.264 requires 50 percent less storage than MPEG-4);
3. Your image resolution (higher the resolution, more storage); and
4. The frames per second you wish to record (more frames, more storage).
The following table approximates the storage capacity needed per day based on 24-hour continuous recording with H.264 compression in a scene with medium activity and complexity. Note that storage will vary based on complexity of scene.
Resolution Frame Rate Storage/day*
VGA 15 fps 3.5GB
VGA 30 fps (full) 6GB
HDTV 720p 10 fps 8.3GB
HDTV 720p 30 fps 18.1GB
Unless mandated by corporate, casino or government policies for video retention, recording continuously for 24 hours a day — especially at full frame rate HDTV video — would be considered highly unusual and frankly a bit overkill. In a typical hosted video scenario, the cameras would be programmed to record to the onsite device at different frame rates and resolutions depending on motion detection, alarm events, certain hours of the day and if network connection is lost. In other words, the above scenario is the maximum you would need per camera per day.
A more realistic hosted video onsite redundancy scenario, for example, would be based on motion detection recording and would look something like this:
Resolution Frame Rate Storage/day*
VGA 15 fps 0.7GB
VGA 30 fps (full) 1.2GB
HDTV 720p 10 fps 1.7GB
HDTV 720p 30 fps 3.6GB
*Both charts were calculated using Axis Design Tool, version 2, based on 30% compression and medium scene activity. For the second scenario, motion detection is assumed at 20%.
If you only plan to leverage onsite storage to protect against potential network failure, then obviously there are plenty of inexpensive storage options you can choose.
Deciding if a Local Surveillance Safety Net is Necessary
If your surveillance system runs on a local area network, the backbone is generally very reliable. With such high uptime, SD cards and NAS devices might be more redundancy than you need — much like wearing suspenders and a belt. But if you are operating in a very demanding application environment or have times of the day (e.g., cash counting shifts) when you cannot afford to lose video, then redundant storage is an absolute necessity. In fact, there are some hosted video integrators today who will not sell a system to a client without some type of backup storage. To them, there’s too much liability at risk.
If you do deploy an onsite storage option, it might make sense to choose a NAS and improve your overall surveillance system by storing crisp, higher resolution video locally. In addition to failover redundancy, you can save on network bandwidth consumption by storing higher frame rate, higher resolution video on the NAS while dual-streaming lower frame rates and lower resolutions to the cloud.