What is RAID and why don’t we use it? RAID is typically a method of using multiple disks together in order to build in some fault tolerance into the storage system.
Not many surveillance systems use RAID or even disk partitions, mainly because of the complexity and added price this adds to a solution and is therefore primarily used in medium to large installations – although the value of a RAID solution will become clear when important video footage is lost. It is always best practice to separate the areas where the Windows Operating system, live video and archive video are stored.
Operating systems do not need fast drives, stability is normally the main requirement, however if the storage space of the OS is reduced and impacted by the video storage the system will crash. Any impact on the OS will impact the whole system, so there needs to be some separation.
* For entry-level surveillance systems it is recommended to at least partition the OS from the recorded video footage.
* In a medium-level installation it is recommended to have a separate hard drive for the operating system and recorded video footage.
* In a large or critical installation we will not only recommended a separate hard drive, but added redundancy such as two hard drives that are mirrors of each other this referred to as RAID 1, so if one drive with the OS were to fail the other drive will still have the necessary information for the system to continue operating.
Live incoming video footage typically needs high performance disks since these disks are constantly working and receiving a continual stream of video data that is analysed for pixel change and then permanently stored to disk. These disks may also buffer several seconds of video for pre and post-event recording. The speed of these disks can also be a limiting factor of the number of cameras or recording bandwidth a system can handle before packets of video footage begin to get lost.
* Entry level sites with low camera count and low bandwidth requirement and tight budget can get away with standard entry level 7200rpm SATA hard drives. Typically these drives have a higher degree of failure so loss of video footage can occur, it will be recommended to look at enterprise class hard drives with a high mean time before failure (MTBF) in more critical installations
* Medium level sites with many megapixel cameras and a higher bandwidth requirement will require faster and more reliable 10 000 to 15 000 rpm SAS hard drives. Some sites where it is critical not to lose information may use two drives for redundancy that are mirrored in a RAID 1 format.
* Large or critical installations with huge amount of megapixel cameras and huge bandwidth requirements that require speed and reliability would opt for high speed SAS drives in a RAID 10 disk array. Raid 10 arrays require four hard drives. The key things to remember about RAID 10 is it has a high fault tolerance, high read/write speed and quick rebuild times for faulty disks. Further information can be obtained on the Internet.
Archiving video is a technique used by some video management systems to move the video data after processing in the live database to a more stable and cost effective storage array. At this point the video has been processed and fast disks are not a prerequisite so less expensive disks such as SATA can be used for more cost effective storage of the video footage.
* Entry level sites may use multiple disks for storage without any redundancy.
* Medium Level sites often use RAID 5 disk arrays which requires a minimum of three disks, and will still function when one disk fails without data loss, however performance is impacted while a new disk is rebuilt which could take a long time.
* Large or critical installations where RAID 6 is the most popular method of storage redundancy require a minimum of four disks and can tolerate two simultaneous disk failures. Added redundancy would be to add hot spares, which are idle disks that will be automatically used when any disks in the array fail.
© Technews Publishing (Pty) Ltd. | All Rights Reserved.
printer friendly version