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Vinchin Blog An introduction to RAID types

An introduction to RAID types


RAID ("Redundant Array of Inexpensive Disks" or "Redundant Array of Independent Disks") is a data storage virtualization technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both.

Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the required level of redundancy and performance. The different schemes, or data distribution layouts, are named by the word "RAID" followed by a number, each scheme, or RAID level, provides a different balance among the key goals.

RAID 0: Combine multiple smaller disks into one large disk, no redundancy, parallel I/O, fastest. RAID 0 is also known as the band set. It is the juxtaposition of multiple disks into one large hard disk. When it stores data, it segments the data by the number of disks and writes the data into those disks at the same time.  

As a result, RAID 0 is the fastest of all levels. But RAID 0 doesn't have redundancy, and if a disk (physically) gets corrupted, all the data becomes unusable.  

RAID 1: Two sets of identical disk systems mirror each other, with no improvement in speed, but allowing single disk errors with the highest reliability. RAID 1 is a mirror. The idea is to store data on the main hard drive while writing the same data on the mirror hard drive. When the primary hard disk (physical) is damaged, the mirror hard disk does the work of the primary hard disk.

With mirrored hard drives for data backup, RAID 1 has the best data security of any RAID level. But its disks are only 50% utilized, the lowest level of disk utilization on any RAID.  

RAID 2: Scatter data into bits or blocks, add Hamming Code, interleaving in the disk array to each disk, and address is the same, that is, in each disk, its data are in the same track and sector. RAID 2 design is the use of coaxial synchronous (spindle the synchronize) technology, access to the data, the action with the whole disk array, in the disk of the same location as the parallel access, and so have the best access time (access time), its bus (bus) is a special design, with large bandwidth (band wide) parallel transmission access of data, and so have the best transmission time (transfer time).  

RAID 3: Data is stored on a different principle than RAID0 and RAID1. RAID 3 is a parity bit that holds data on one hard disk, and data is segmented onto the rest of the hard disks. It stores Numbers in parallel like RAID 0, but not as fast as RAID 0. If the disk (physically) is corrupted, just replace the broken hard drive, and the RAID control system will reconstruct the data on the broken disk in the new disk-based on the data check bits of the disk. However, if the check disk (physical) is corrupted, all of the data becomes unusable.

RAID 4: Using a parity disk, sector data segmentation, each disk at the same location as a parity block formed by the segmentation, on the parity disk. This method can perform different reads on different disks in parallel and greatly improve the read performance of disk array. However, when writing data, due to the limitation of the calibration disk, it can only be done once at the same time. Start all data read by the disk to form all data segments of the same calibration segment, and make calibration calculation with the data to be written before writing.

RAID 5: Writes data to the disks in the array, and the parity data is stored on each disk in the array, allowing individual disks to fail. RAID 5 also USES the checksum bits of data to keep data safe, but instead of storing the checksum bits of data on individual hard drives, it interactively stores the checksum bits of data segments on each hard drive. In this way, any corrupted hard drive can be reconstructed from the check bits on other hard drives. The utilization of the hard disk is n-1.

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