A: From a CCTV perspective, digital storage of video images on a hard drive (typically using a DVR) is no different from other media stored on a conventional PC. Consequently the system processor makes decisions about where data is stored, depending on available disk space. With RAID configured systems, video data is managed in a more logical and secure fashion. The ultimate aim is to achieve a much greater level of data protection and provide disaster recovery in the event of disc failure.
A: RAID 0 systems are often used to increase overall archive capacity, and thus provide cost efficiency. However, RAID 0 systems don’t provide any extra data security; for that RAID 1 or RAID 5 configurations are commonly used. With RAID 1, all CCTV images are written in duplicate (requiring at least two disks). This doubles the number of disks needed, but it also means that if one disk fails, or if video evidence in impounded, no images are lost because the mirrored archive is still available. RAID 5 is a little more refined. Data for the images is striped over several disks. The system also produces and stores additional parity data. If a disk fails, it can use this parity data to rebuild the images that would otherwise be lost. There is a disadvantage with RAID5 in that if the data is impounded by the police, there may not be a ‘mirrored’ version of the removed data available.
A: Removable storage is very useful when the police need to impound images for use as evidence, since they don’t need to impound the whole recorder. However, this advantage is lost if a mixture of fixed and removable storage is used as, in these cases, the police will always want to impound the recorder and the removable storage. It’s also worth noting that removable storage is less secure than internal storage. It’s a lot easier to make a disk cassette ‘disappear’ than a DVR!
A: Certainly, and this is a common approach where large amount of data is archived. It’s important to make sure that you get the right interface for the application. There are two in common use – NAS and SCSI – each offering different benefits. Internal RAID management systems are, of course, also offered with high end DVRs.
