[Data Source] What does RAID Mean? Raid applications

A disk array is an out-of-memory sub-system with a large capacity. It is usually called a redundant display RAID (redundanar ray of Inexpensive Disk). It is based on certain rules by many hosts or optical disk machines, such as striping, declustering, and Interleaving to back up data and improve the performance of disk arrays used by computers in China. Through the control and management of the array controller, the disk array system can connect several, dozens or even hundreds of disks into one disk, so that its capacity can reach hundreds to GB. Raid, a cheap redundant disk array, is short for Redundant Arrays of Independent Disks.

Category

Disk Arrays can be divided into soft arrays and hard arrays. The soft array is through the softwareProgramThe computer processor can only provide the most basic RAID fault tolerance function. A hard array is an independently operated hardware (array card) that provides control and computing functions for the entire disk array. The card has an independent processor and does not rely on the CPU resources of the system, all the fault tolerance functions are supported, so the functions and performance of the hard array are better than those of the soft array.

Level

As a high-performance storage technology, raid has been widely used. The level of raid has evolved from the concept of raid to many levels, but the four most commonly used levels are 0, 1, 3, and 5. The following describes the four levels.

RAID 0

Merge multiple disks into a large disk with no redundancy. Parallel I/O provides the fastest speed. It is used to combine multiple disks to form a large hard disk. When storing data, the data is segmented by the number of disks and written into these disks at the same time. Therefore, RAID 0 is the fastest in all levels. However, RAID 0 does not have redundancy. If a disk (physical) is damaged, all data cannot be used.

Raid 1

The two groups of identical disk systems make images for each other, but the speed is not improved, but a single disk error is allowed, with the highest reliability. Raid 1 is an image. The principle is to store data on the primary hard disk and write the same data on the image hard disk. When the primary hard disk (physical) is damaged, the image hard disk replaces the primary hard disk. Because there is an image hard disk for data backup, the data security of RAID 1 is the best at all RAID levels. However, the disk utilization is only 50%, which is the lowest utilization of all RAID disks.

RAID 3

The principle of data storage is different from RAID 0 and RAID 1. RAID 3 uses a hard disk to store the parity of data, and data is stored in segments on other hard disks. It stores data in parallel like RAID 0, but the speed is not faster than RAID 0. If the data disk (physical) is damaged, as long as the bad hard disk is replaced, the raid Control System reconstructs the data on the bad disk according to the Data check bit of the disk. Although the security of data without images is high, the hard disk utilization is greatly improved by using a separate verification disk, which is n-1. However, the disadvantage is that the hard disk stores the checkpoint, and the workload will be very high, because each write operation will write the generated verification information to the disk, while the load on other disks is relatively small, this will have a certain impact on performance.

RAID 5

On the basis of RAID 3, RAID 5 has made some improvements. When writing data to the disk in the array, the parity data is evenly stored on each disk in the array, allowing an error on a single disk. RAID 5 also ensures data security by the Data check bit, but it does not store the data check bit on a separate hard disk, but stores the check bit of the Data Segment on each hard disk. In this way, damaged data can be rebuilt based on the check bit on other hard disks. The hard disk utilization is n-1.

Raid is the abbreviation of Redundant Array of Independent Disks ).

Summary

To put it simply, raid combines multiple independent hard disks (physical hard disks) in different ways to form a hard disk group (logical hard disks ), this provides higher storage performance than a single hard disk and Data Backup technology. RAID levels is used to form disk arrays ). The data backup function is used to restore damaged data once the user data is damaged, thus ensuring the security of user data. In the user's view, a disk group is like a hard disk, which can be partitioned, formatted, and so on. In short, the operations on the disk array are the same as those on a single hard disk. The difference is that the storage speed of the disk array is much higher than that of a single hard disk, and automatic data backup can be provided.

Features

Two major features of RAID technology: speed and security. Due to these two advantages, RAID technology was applied to hard disk systems with SCSI interfaces in advanced servers in the early days, with the development of computer technology in recent years, the CPU speed of PC has entered the GHz era. The hard disks of the IDE interface are also lagging behind, and ata66 and ata100 hard disks are successively released. This makes it possible to apply RAID technology to low-end or even personal PCs. Raid is usually implemented by the RAID Controller in the hard disk array or the RAID card in the computer.

With the continuous development of RAID technology, we now have seven basic RAID levels, ranging from RAID 0 to raid 6. In addition, there are some basic raid-level combinations, such as raid 10 (a combination of RAID 0 and RAID 1) and raid 50 (a combination of RAID 0 and RAID 5. Different RAID levels represent different storage performance, data security, and storage costs. However, we usually use the following raid forms.

(1) RAID 0

(2) RAID 1

(3) RAID 0 + 1

(4) RAID 3

(5) RAID 5

There are three main factors to choose a raid level: availability (data redundancy), performance, and cost. If availability is not required, select raid0 for optimal performance. If availability and performance are important and cost is not a major factor, select RAID 1 based on the number of hard disks. If availability, cost, and performance are equally important, select raid3 and RAID5 based on the average number of data transmission and hard disks.

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