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Written By: Ontrack
Date Published: 08 November 2023 06:12:42 EST
The definition of RAID is in the name of the system itself. Standing for Redundant Array of Independent Disks, RAID literally means redundant bundling of independent disks – a cluster of multiple hard drives to get a single logical partition. Depending on the purpose, RAID increases the performance of accessing and writing data, while improving the security of the information.
RAID is a technology that supports the use of two or more hard drives in various configurations for the purposes of achieving greater performance, reliability and larger volume sizes through the use of consolidating disk resources and parity calculations.
A number of standard configurations were designed which are referred to as levels. There were five RAID levels originally created, but many more variations have evolved, notably several nested levels and many non-standard levels (mostly proprietary).
So, what do the RAID levels mean? The numbers simply refer to the configuration of the RAID. Knowing that all RAID systems store data efficiently, the choice of system will be based on your own personal or organisational needs. RAID 1, for example, meets the needs of performance and reliability. RAID 5 is a good choice if you are looking for both performance and fault tolerance.
The result of their research has formed the basis of the complex RAID storage systems that exist today. Today, IBM holds the intellectual property rights to RAID 5. The design of the RAID storage system was aimed at improving the performance, recovery, reliability, and scalability of storage. The result was a unique redundancy concept that offers data recovery capabilities in the event that a drive fails in the system. In fact, RAID controller cards have acquired the ability to continue reading and writing data even if a disk is offline'.
A RAID combines physical hard disks into a single logical unit by using either special hardware or software. Hardware RAID solutions can come in a variety styles, from built onto the motherboard or add in cards, up to large enterprise NAS or SAN servers. With these setups the operating system is unaware of the technical workings or the RAID. Software solutions are typically implemented in the operating system.
There are three key concepts in RAID:
Different RAID levels use one or more of these techniques, depending on the system requirements.
RAID is traditionally used on servers, but can be also used on workstations. The latter is especially true in storage intensive computers such as those used for video and audio editing.
Our engineers agree that recovering RAID arrays is one of the most difficult technical aspects of data recovery. The evaluation of a RAID system recovery is actually the combination of two very important steps:
The first, and the longest, is the reassembly of the matrix. When the Ontrack Data Recovery engineers reassemble the logical system, they thoroughly research how the data is organised across all disks. They then know the order of disks and the arrangement of data blocks and parity blocks. This investment in time is necessary to determine the original configuration and obtain a quality recovery,
The second step is to work on the logical file system. Current enterprise log file systems are extremely complex. If the RAID array is down, there will be thousands of errors within the file system. Ontrack Data Recovery engineers will verify and confirm that the matrix is structured correctly before copying any data. This extra step guarantees a quality recovery.
The logical RAID system configuration splits the data in tapes across all physical disks. This makes it possible to have a balanced data rate on all the disks; instead of having a disk that does all the work of reading and writing the data, all the disks work together. The data is therefore distributed over all the physical disks.
Redundancy in a current RAID 5 configuration is the result of using a Boolean mathematical function called "Exclusive OR" (XOR). This is commonly referred to as parity. The XOR function is a logical binary process. It is best to consider the parity as a combination of the data blocks of the other disk. Each byte that is written in a data block is calculated relative to the other data blocks. The parity obtained is written in the parity block for this given band. This calculation will always work, regardless of a missing data block. However, the calculation will not work if two blocks are missing, which is one of the limitations of RAID 5; it will not provide adequate redundancy if two or more disks fail.
As previously indicated, the controller board splits the data into tapes and also performs the XOR function on that data. The amount of logic computations performed by the controller every second is impressive. Current RAID controllers are highly sophisticated hardware systems, including SDRAM processors and memory banks specifically designed for performance and redundancy.
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