RAID technology key knowledge and RAID features

The RAID technology has three main features:

First, by striping the data on the hard disk, it realizes block access to data, reduces the mechanical seek time of the hard disk, and improves data access. speed.

Secondly, by reading several hard disks in an array at the same time, the mechanical seek time of the hard disk is reduced, and the data access speed is improved.

Third, the redundancy protection of data is realized by mirroring or storing parity information.

Frequently used RAID arrays are mainly divided into RAID 0, RAID 1, RAID 5 and RAID 0+1.

1, RAID0: Striping

RAID 0 is also called striping, which writes data to multiple disks like strips. These strips are also called "blocks" ; Striping enables simultaneous access to data on multiple disks, balancing I/O load, increasing data storage space and speeding data access. RAID 0 is the only RAID technology that does not have redundancy, but RAID0 is less expensive to implement. If one of the disks in the array fails, all data in the array is lost. To restore RAID 0, only replace the bad hard drive and restore data from the backup device to all hard drives.

RAID0 can be implemented in both hardware and software. Implement RAID0 with a minimum of 2 hard drives. For the system, the data is stored on all hard disks in a distributed manner. When a hard disk fails, the data is completely lost. RAID 0 provides high hard disk I/O performance and can be implemented in either hardware or software.

2, RAID 1

RAID 1 is also known as disk mirroring. The system writes data to both hard disks at the same time, but it acts as a logical disk in the operating system. So if one hard disk fails, the other hard disk still retains a complete data, and the system can still work as usual. The system can read data from two hard disks at the same time, so it will increase the speed of hard disk reading; however, because the data needs to be repeated once in the system, it will affect the speed at which the system writes data. The utilization of hard disk capacity is only 50%.

3, RAID 0+1

Mirror the RAID0 array. This is a Dual Level RAID, also known as RAID level 10. It is the two sets of hard disks to do RAID 0 first, which constitutes two large-capacity logical hard disks, and then each other is "Mirror". Each time data is written, the disk array controller writes the data to both sets of "large-capacity array disk groups".

Like RAID level 1, although its hard disk usage is only 50%, it is the most efficient way to plan.

4, RAID 5

is developed on the basis of RAID 3 and RAID 4, it inherits their data redundancy and striping characteristics, and data verification Information is evenly stored on all hard disks in the array. The system can simultaneously read and write all the hard disks in the array, which reduces the time delay caused by the mechanical system of the hard disk and improves the I/O capacity of the disk system. When a hard disk in the array is bionic, the system can be saved on other hard disks. The parity information recovers the data of the failed hard disk and continues to work normally. The above describes the RAID technology.