HD Video Surveillance
fact that the HD video does not have to hauled across the entire network. It can be archived locally, leaving a lower resolution stream to be transmitted for viewing purposes. The HD stream only needs to be pulled back to a control point if an event has occurred. There are two main approaches to archiving
video. One is to move footage from the NVR to a storage server. The other is to capture footage at the edge (the location of the cameras and/or encoders), only retrieving it when there is a need to do so.
The first scenario makes use of dedicated
archiving hardware, whilst the latter increasingly uses memory cards, with devices supporting integral card slots.
A dedicated approach
The storage market has caught on to the fact that video surveillance generates high levels of data, and that data needs to be stored securely. The result has been an increase in the number of offerings being presented to the security sector.
Whilst this seems positive on the surface of things, Benchmark has seen some manufacturers using the security sector as a dumping ground for outdated technology. It is important that those specifying such solutions ensure that the manufacturer has done something to serve the needs of the security sector, rather than just paying it lip-service as a part of their stock clearance exercise. Increasingly, credible manufacturers of NVRs and DVRs are also offering additional archiving solutions. However, some storage sector products do benefit from significant economies of scale! Often, the choice is NAS (network attached
storage) or SAN (storage area network). NAS devices are single units that sit on the network and work on a file basis. When connected, the system sees them as a type of file server. SANs are made up of a number of disks - referred to as a disk array - which work on a disk block basis. In essence, the operating system sees and treats them as drives, handling its own file hierarchy management. Typically, implementation of
SAN set-ups requires more configuration than NAS options. For redundancy in video surveillance, the two main offerings are RAID1 and RAID5. There are many other options, but because of the throughput of video surveillance systems these two are considered to be the most robust. RAID1 simply mirrors drives. Two drives are used to record one drive’s worth of data. The contents of each disk would be identical, so if one disk fails, the second retains the data. RAID5 uses a minimum of three drives, and video data - along with parity data - is spread across the disks. If a single disk fails, then the data can be rebuilt. RAID1 offers good data security, but does double the cost of storage. RAID5 can support any single drive failure, but can have increased read/write requirements.
On the cards
Before considering removable media, it’s worth looking at some myths about the available options. Many feel that memory sticks and memory cards offer poor reliability. We’ve all had cards fail; we’ve all lost data or had connection problems. When you buy memory, you get what you pay for. Also, you need to exercise basic care when inserting or removing cards. SD cards in all their forms are the most common memory cards that are built in to security devices. You can buy SD cards that will probably fail in a few weeks if used a lot, and you can buy SD cards that are reliable. The latter obviously cost more.
Benchmark often uses high capacity SDHC
cards. Compared to other options, they are not the cheapest. That said, on a GB basis they are low cost compared to hard drives! The cards have been used heavily over a few years, in a wide range of environments from over 40°C and extreme humidity, down to well below freezing. They have been used for data, images and HD video. Once, in a fit of clumsiness, one was bent in half, and still retains a severe kink. All still work perfectly. Increasingly, video surveillance devices are including SD card slots. Use of these for local
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