What does hard disk RAID Mean? What is the purpose?

I. Raid Definition
RAID (Redundant Array of independent disk independent redundant disk array) technology is the University of California, Berkeley, 1987

It was initially proposed to combine small and low-cost disks to replace large and expensive disks. At the same time, it was hoped that access to data would not be damaged when the disk fails.

Develop a certain level of data protection technology. Raid is a Redundant Array composed of multiple low-cost disks.

Is an independent large storage device. Raid can give full play to the advantages of multiple hard disks, increase the speed and capacity of hard disks,

The Fault Tolerance function is provided to ensure data security and ease of management. You can continue to work if any hard disk is faulty,

The disk will not be damaged.
Ii. Several raid Modes
1. raid0
That is, data stripping data sharding technology. RAID 0 can connect multiple hard disks into a larger hard disk group, which can improve the disk

Disk performance and throughput. RAID 0 has no redundancy or error repair capability, and the cost is low. It requires at least two disks, usually only in the logarithm

It is used only when the security requirements are not high.
(1) RAID 0 is the easiest way
It means to use X hard disks in the form of hardware through the smart disk controller or the disk drive in the operating system.ProgramBy Software

Form an independent logical drive, which is X times the capacity of a separate hard disk and is written to each disk in sequence when writing computer data.

When the space of a disk is exhausted, data is automatically written to the next disk. The advantage is that the disk capacity can be increased.

The speed is the same as that of any disk. If any disk fails, the entire system will be damaged and reliable.

Is to use a hard disk separately 1/N.
(2) Another RAID 0 Method
Create a zone set using N hard disks with a reasonable size. It is best to assign a dedicated disk controller to each hard disk.

When reading and writing computer data to N disks at the same time, the speed is increased by N times. Improve system performance.
2. Raid 1
Raid 1 is called a disk image: It mirrors data from one disk to another, ensuring maximum performance without affecting the performance.

The system has high data redundancy capability in terms of reliability and maintainability, but the disk utilization is 50%, so the cost is the highest and is mostly stored.

Important data. Raid 1 has the following features:
(1) Each disk in Raid 1 has a corresponding image disk, and data is synchronized to the image at any time. The system can

Read data from any disk on the image disk.
(2) the space used by the disk is only half of the total disk capacity, and the system cost is high.
(3) As long as there is at least one disk in any one of the system's image disks, you can even ask questions in the case of half of the number of hard disks.

The system can run normally.
(4) If the RAID system is no longer reliable due to a hard disk failure, the damaged hard disk should be replaced in time; otherwise, the remaining image disks will also appear.

The system crashes.
(5) After the new disk is changed, the original data will need a long time synchronization Image, and external access to the data will not be affected.

The performance of the entire system has declined.
(6) RAID 1 has a large disk controller load. Using Multiple disk controllers can improve data security and availability.
3. raid0 + 1
Combined with raid0 and raid1 technologies, each disk has its physical image disk, which provides full redundancy.

Force, allows one or more disk failures without affecting data availability, and has the ability to read/write quickly. Raid0 + 1 to be created in the disk image

There must be at least four hard disks in the band.
4. raid2
When writing data, the computer saves the bit of data on a disk, and calculates the Hamming checkcode for each bit of data.

Save another set of disks, because the Hamming code can correct errors in case of data errors, to ensure that the output is correct. But Hamming Code

With data redundancy technology, the speed of output data depends on the slowest disk in the drive group. The raid2 controller is easy to design.
5. raid3: parallel transmission with parity Codes
RAID 3 uses a dedicated disk to store all the verification data, and creates read/write operations with Scattered Data in the remaining disk

. When reading data from an intact RAID 3 system, you only need to find the corresponding data block in the data storage disk for read operations. However

When writing data to raid 3, you must calculate the check value of all data blocks in the same zone as the data block and re-write the new value

Check block, which increases the system overhead. When a disk fails, all data blocks on the disk must be verified again.

Create. If the data block to be read is located in the damaged disk, you must read all other data blocks in the same zone at the same time,