What is RAID (Redundant Array of Independent Disks)? How does it work?

 

RAID or redundant arrays of storage disks store the same data in different locations. Multiple hard disks store this data and protect it in the event of a drive failure. Redundancy, however, is not present at every RAID level.

RAID is typically used to maintain the speed and performance of a computer’s disk storage. It is often used on high-performance computers and servers.

History of RAID

The term RAID was first coined in 1987. David Patterson, Randy Katz and Garth A. It was written by Gibson in a 1988 technical report. The report was entitled “A Case for Redundant Arrays of Expansive Disks (RAID).”

The authors opined that the performance of the top disk drives of the time could be improved by using a range of cheaper drives. With the use of redundancy, the reliability of the RAID array changes the reliability of any single disk drive.

The word ‘cheap’ was abbreviated to ‘independent’ by industry vendors. This was to avoid the effects of low cost.

How RAID works

Using RAID, data is placed on multiple disks. Correspondingly, the input / output operations overlap in a balanced manner. This, in turn, improves the performance of the system.

For the operating system, the RAID array looks like a logical hard disk. Techniques used to operate RAID include disk stripping and disk mirroring.

Disk mirroring

With mirroring, two RAID arrays can have two drives with identical data. Therefore, one drive continues to work even when another crashes.

Disk stripping

Similarly, the stripping units partition the drive’s storage space. The unit can be sector or 512 bytes. It could alternatively have several megabytes of storage space. The process is striped.

The straps of each disc are connected to each other. They are addressed in the prescribed order.

The size of the stripes depends on the application for which the RAID is used. For a single user system that contains large records, the stripes are typically small. This ensures that the record is spread across the disk. It also makes it easier to access records, and all discs can be read at once. An example of RAID in which small stripes are used to store scientific images or medical records.

However, in the case of a multiuser system, the belt size should be wider. This allows the strip to easily accommodate the maximum size record. Correspondingly the user can get the overlapped disk I / O across the drives.

Both disk stripping and disk mirroring can be combined on a RAID array. Both are used together in RAID 01 and RAID 10.

RAID controller

The RAID controller defines the level of abstraction between the physical disk and the OS. It therefore protects data in the event of a crash and also improves performance.

The RAID controller can be used for both hardware and software-based RAID arrays. For hardware-based RAID production, the array is powered by a physical controller. This could be in the form of a PCI card, or it could be part of a motherboard.

If the RAID array is software-based, the RAID controller has the same functionality as the hardware-based RAID array. But it uses the resources of the hardware system.

The benefits of RAID

The main advantages of RAID are cost-saving, resilience and performance. RAID is typically an improvement over the performance of a single hard drive. It depends on how the RAID is configured.

After a crash, RAID increases the reliability and speed of the computer.

With RAID 0, the files split. They are then distributed throughout the drive. All drives work on the same files. Reading and writing tasks are consistently faster than using the same drive.

Even with RAID 5, arrays are split into data sections. But other drives are also dedicated to equality. When a non-parity drive fails, the parity drive sees what is working. Parity Drive thus removes the data present on the failed drive. As a result, RAID 5 shows high availability.

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