Introduction to RAID

A RAID disk array is composed of many independent disks, combined into a large-capacity disk group, using the bonus effect of individual disks to provide data to enhance the performance of the entire disk system. Using this technology, the data is cut into many sections and stored on each hard disk.
Disk arrays can also use the concept of parity check. When any hard disk in the array fails, data can still be read. When data is reconstructed, the data is recalculated and placed in a new hard disk.

Disk array classification

Disk array card : It can provide solutions for performance, data protection, reliability, availability and manageability.
Software simulation : The performance of the disk subsystem will be reduced, some of which are relatively large, up to about 30%. Therefore, it will slow down the speed of the machine and is not suitable for servers with large data traffic.

Common RAID levels

RAID 0

RAID 0 is the simplest form of building a disk array. It only needs more than two hard disks, which is low cost and can improve the performance and throughput of the entire disk. RAID 0 does not provide redundancy or error repair capabilities, but the implementation cost is the lowest.
The biggest disadvantage is that if any one hard disk fails, the entire system will be destroyed.

RAID 1

RAID 1 is called disk mirroring. The principle is to mirror the data of one disk to another disk. That is to say, when data is written to one disk, a mirror file will be generated on another idle disk without affecting performance. To ensure the reliability and repairability of the system to the greatest extent, as long as there is at least one disk in any pair of mirror disks in the system, the system can run normally even when half of the hard disks have problems. When it fails, the system will ignore the hard disk and use the remaining mirrored disk to read and write data, which has good disk redundancy capabilities.
The biggest shortcoming is that the performance drops, the cost rises, and the disk utilization rate is 50%.

RAID 1+0

The combination of RAID0 and RAID1, when we use RAID 1 alone, there will be problems similar to using RAID 0 alone, that is, data can only be written to one disk at the same time, and all resources cannot be fully utilized. To solve this problem, we can create a stripe set in the disk mirroring. Because this configuration method combines the advantages of striping and mirroring, it is called RAID 1+0. Combining RAID0 and RAID1 technologies, in addition to data distribution on multiple disks, each disk has its own physical mirror disk, providing full redundancy, allowing one or less disk failures without affecting data availability, and having fast read /Writing ability. RAID 1+0 must have at least 4 hard disks in the disk mirroring.

RAID 5

RAID 5 does not back up the stored data, but stores the data and the corresponding parity information on each of the disks that make up the RAID5, and the parity information and the corresponding data are stored on different disks. When one of the RAID5 disk data is damaged, use the remaining data and the corresponding parity information to recover the damaged data. RAID 5 has "write loss". RAID 5 has a very high read efficiency and average write efficiency.

Toss notes-server group RAID