University Of East Anglia
RPC Logistics need for High Security
Check Your Security Ltd is an East of England based systems design and build integration company specialising in CCTV/IP-CCTV, structured cabling systems, Fibre cabling, Access control and Intruder security systems.
RAID
What is RAID and why?In computing, a redundant array of independent disks (more commonly known as a RAID) is a system of using multiple hard drives for sharing or replicating data among the drives. Depending on the version chosen the benefit of RAID is a one or more of increased data integrity, fault-tolerance, throughput or capacity compared to single drives. In its original implementations (in which it was an abbreviation for "Redundant Array of Inexpensive Disks"), its key advantage was the ability to combine multiple low-cost devices using older technology into an array that together offered greater capacity, reliability, and/or speed than was affordably available in singular devices using the newest technology RAID stands for redundant array of independent disks At the very simplest level, RAID is one of many ways to combine multiple hard drives into one single logical unit. Thus, instead of seeing several different hard drives, the operating system sees only one. RAID is typically used on server computers, and is usually implemented with identically-sized disk drives. With decreases in hard drive prices and wider availability of RAID options built into motherboard chipsets, RAID is also being found and offered as an option in higher-end end user computers, especially computers dedicated to storage-intensive tasks, such as video and audio editing or in our case CCTV.
We at Check Your Security Limited offer as an option the connection of a RAID as opposed to a single, or collection of disks. Depending on the type and size of RAID required determines how the RAID is implemented either direct from the motherboard as an additional card or as a sepearte dedicated storage device.
RAID is sepearted into levels each with its own attributes and uses. The appropriate RAID level required for your project would be discussed during the design stage but essentially they allow for better performance, fault tolerance or a combination. Some configurations even allow for Hot Swaps of faulty disks i.e. replacing a faulty disk on a live system.
A selection of commonly used levels are detailled below:
RAID0
RAID 0 (also known as a striped set) splits data evenly across two or more disks with no parity information for redundancy. It is important to note that RAID 0 was not one of the original RAID levels, and is not redundant. RAID 0 is normally used to increase performance, although it is also a useful way to create a small number of large virtual disks out of a large number of small physical ones.
RAID1
RAID 1 creates an exact copy (or mirror) of all of data on two or more disks. This is useful for setups where redundancy is more important than using all the disks' maximum storage capacity. The array can only be as big as the smallest member disk, however. An ideal RAID 1 set contains two disks, which increases reliability by a factor of two over a single disk, but it is possible to have many more than two copies. Since each member can be addressed independently if the other fails, reliability is a linear multiple of the number of members. RAID 1 can also provide enhanced read performance, since many implementations can read from one disk while the other is busy. To truly get the full redundancy benefits of RAID1, you also want to have independent disk controllers, one for each disk. Some refer to this practice as "splitting" or "duplexing."
RAID5
RAID 5 combines the mirror and stripe of RAID 0 and RAID1 together with a separate parity check of the data held on the disks. should a disk fail in the array, the parity blocks from the surviving disks are combined mathematically with the data blocks from the surviving disks to reconstruct the data on the failed drive "on-the-fly". This is sometimes called Interim Data Recovery Mode. The computer knows that a disk drive has failed, but this is only so that the operating system can notify the administrator that a drive needs replacement; applications running on the computer are unaware of the failure. Reading and writing to the drive array continues seamlessly, though with some performance degradation.
RAIDs can be combined e.g. RAID 0 + 1 to get a mirror of stripes. This is not the same as RAID 5 as the parity block is not created.
JBOD
Although a concatenation of disks (also called JBOD, or "Just a Bunch of Disks") is not one of the numbered RAID levels, it is a popular method for combining multiple physical disk drives into a single virtual one. As the name implies, disks are merely concatenated together, end to beginning, so they appear to be a single large disk.Similar to RAID but not really a RAID is JBOD or Just a Bunch Of Disks is simply the joining together or concatentaion of disks. In this sense, concatenation is akin to the reverse of partitioning. Whereas partitioning takes one physical drive and creates two or more logical drives, JBOD uses two or more physical drives to create one logical drive.
In that it consists of an Array of Inexpensive Disks (no redundancy), it can be thought of as a distant relation to RAID. JBOD is sometimes used to turn several odd-sized drives into one useful drive. Therefore, JBOD could use a 3 GB, 15 GB, 5.5 GB, and 12 GB drive to combine into a logical drive at 35.5 GB, arguably more useful than the individual drives separately.
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