Digital CCTV Storage Basics
Storage capacity can range from one single hard drive up to a SAN (Storage Area Network) consisting of a number of disk array (RAID) units on a switched fabric network.
To calculate the storage capacity required, the following information is needed (the provided sample parameters will be used in the configuration discussed below):
File size of each frame - 40KB
Frame rate (number of frames recorded in one second) - 3 frames per second
Number of cameras connected - 99 security cameras
Continuous Recording capacity- 1month
If data from 100 cameras has to be kept for 31 days, the Digital Recording System (DRS) will overwrite data recorded on the first day with data recorded on the 32nd day. On the 33rd day, the DRS overwrites the data recorded on the second day and so on. In this way, the last 31 days of data will always be stored.
CCTV Engineers connecting CCD Security Cameras to Digital Storage Recorders
Most DRSs are able to connect multiple cameras. In the example show in Diagram 2, five DRSs are connected 100 cameras (20 cameras connected to one DRS). Each DRS is then linked to the data storage (RAID system) using Fibre Channel cables.
When multiple DRSs are connected to one or more RAID systems, Fibre Channel optical cables are the preferred choice as they make the connections more flexible, easier, and enable connectivity over a longer distance. However, if each DRS has its own dedicated RAID system, SCSI cables can be used as well.
The security aspect of sharing the stored data must also be considered. Sharing One RAID between Multiple DVRs (Digital Recorders). The DRS normally uses its own CPU, utilizing Windows, or Linux. The greater part of operating systems will not presume that the same storage capacity is being shared with any others. When one RAID system is shared by several DRSs, it is imperative to ensure they do not see each other. The CCTV Engineer can create multiple RAID 5 data volumes from the RAID system. When one data volume is defined for each DRS, each volume will need the capacity of one drive for RAID 5 operation. Therefore the more RAID 5 volumes defined, the more drives are taken up by the RAID5 operation. In order to reduce the number of drives used by the RAID5 operation, it is recommended to divide one RAID5 volume into multiple partitions, and then allow each DRS to access its own partition. Complicated systems require access control in order to access the stored data anytime, anywhere. This is available through the WWN (World Wide Name) access control function from the Fibre Channel switch.
One RAID system is storing data for five DRSs without the need for further software .
Hard Disk Options are IDE, SCSI, SATA, or Fibre Optics
There are various types of hard disk drives in the market today—IDE (PATA, parallel ATA), SATA (serial ATA), SCSI, and Fibre—and there RAID systems available based on each type of drive. Many RAID storage vendors only offer products using one drive type.
This can be a major disadvantage as it reduces the overall number of available options and solutions that a CCTV company can offer their customers. Some manufacturers provide a complete range of products which enables them to offer diverse solutions that utilize all of the available drive types.
But regardless of the drive type selected, the systems are designed to appear identical to the operating system and user. This gives customers maximum flexibility to choose products that exactly meet their budget and technical requirements without sacrificing RAID functionality.
Because RAID features are provided by the RAID controller, RAID operations are similar between IDE, SATA, SCSI and Fibre drive RAID systems. The differences between the systems are based on the different characteristics of the drive types themselves, especially in terms of maintenance, expandability, and cost. User Scenario: Handing Proof to theAuthorities.
If an event (e.g., a crime) has occurred, it is vital to be able to quickly provide the evidence to the police for investigation. The evidence taken by the police must be unique (i.e., must be the only copy), which means the site is not allowed to keep a duplicate.
Security CCTV systems require the implementation of downloadable media in order to have an easy method for delivering the proof. Specific requirements will vary from country to country or between sites. When an analog CCTV system is used, the evidence is simply the VCR tapes. There is usually only one copy (the master copy) of the tape. The authorities take this main copy and the camera operator loads in a replacement tape. When a digital CCTV system is implemented, various key points concerning the presentation of evidence need to be considered
The Mainr copy Cost of the removable media Time to retrieve the captured images Most RAID systems are designed so that all of the drives are easily removable. Some systems have "Configuration-on-Disk," which means that when all of the disks from one RAID system are removed and placed in another RAID system, the RAID's logical drive and data can still be recognized and accessed. If the police have an identical RAID system, the disks from the Security surveillance system can be removed and installed into the police system. The evidence can then be retrieved immediately, with no reduction in quality. Care must be taken when transporting the disks between sites.
If the drives are removed by the police, CCTV operators can just install replacement drives to continue running the CCTV operation. Another option is to take the complete RAID system to the police site. In the example described above, a 100-camera CCTV system requires only one RAID system, which can easily be transported by car.
As DRSs usually have a built-in hard drive, the software should be able to record and store the images captured from the time the Master Copy was taken off-line to when the Replacement System was brought on-line. As soon as the Replacement System is on-line, this data is immediately moved from the DRS's built-in hard drive onto the RAID system. At any given time, only one of the RAID systems is switched on. The data is normally stored in the RAID system labeled - Master Copy. When the police take the Master Copy, the operator simply switches on the "Replacement System" and the CCTV operation can then continue immediately. Digital CCTV was designed and developed to improve upon the existing analog CCTV installations by providing pictures with a higher resolution and better image quality and by offering immediate and random access capability.
Logically digital CCTV designers will want to balance the solution based upon many different parameters including product features, timing, cost, etc. On the data storage side, RAID manufacturers can help by providing a variety of high quality, cost-effective storage products which will satisfy the requirements of all CCTV applications, regardless of size or budget.
