Raid 1-6

RAID 0

RAID 0 is also called a zone set. It concatenates more than two disks to form a large-capacity disk. When data is stored, segments are distributed and stored in these disks. Because read/write operations can be performed concurrently, RAID 0 is the fastest speed at all levels. However, RAID 0 has neither redundancy nor Fault Tolerance capabilities. If a disk (physical) is damaged, all data will be lost, which is at the same level as jbod.

Raid 1

Two or more groups of N disks serve as images for each other. In some multi-threaded operating systems, the read speed is equal to the number of hard disks theoretically, and the write speed is slightly reduced. As long as a disk is normal, it can be maintained with the highest reliability. Raid 1 is an image. Its 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, no matter how many disks are used as RAID 1, only the capacity of one disk is counted, which is the lowest disk utilization among all raid.

Raid 2

This is an improved version of RAID 0. It uses hamming code to encode the data, partition the data into independent bits, and write the data to the hard disk separately. Because the Error Correction Code (ECC, Error Correction Code) is added to the data, the overall data capacity is larger than the original data, and raid2 requires at least three disk drives to operate.

RAID 3

Bit-interleaving (Data staggered storage) technology is used. It needs to separate data bits by encoding and then store them in the hard disk separately, and the same bit is checked and then stored separately in the hard disk, however, because the bits in the data are scattered on different hard disks, even if you want to read a small segment of data, all hard disks may need to work, therefore, this type is suitable for reading large amounts of data.

Raid 4

It differs from RAID 3 in that it exists in hard disks in blocks when partitioning, however, each data access request must retrieve the corresponding same-bit data from the disk with the same-bit check. Due to the frequent use, the hard disk loss may increase. (Block interlace technology, block interleaving)

RAID 5

Raid Level 5 is a storage solution that combines storage performance, data security, and storage costs. It uses the Disk Striping technology. RAID 5 requires at least three hard disks. Instead of backing up the stored data, RAID 5 stores the data and the corresponding parity information on each disk that makes up RAID 5, in addition, the parity information and the corresponding data are stored on different disks. When a disk data in RAID 5 is damaged, you can use the remaining data and the corresponding parity information to restore the damaged data. RAID 5 can be understood as a compromise between RAID 0 and RAID 1. RAID 5 can provide data security protection for the system, but its security level is lower than that of the image, and the disk space utilization is higher than that of the image. RAID 5 has a Data Reading Speed similar to RAID 0, but because of an additional parity information, the Data Writing speed is slightly slower than writing data to a single hard disk, using "Write-back high-speed cache" can significantly improve performance. At the same time, because multiple pieces of data correspond to one parity information, the disk space utilization of RAID 5 is higher than that of RAID 1, and the storage cost is relatively low.

Raid 6

Compared with RAID 5, raid 6 adds the second independent parity information block. Two independent parity systems use different algorithms, and the data reliability is very high. Even if the two disks are invalid at the same time, the data usage will not be affected. However, raid 6 needs to allocate more disk space to the parity check information, which has a greater "Write loss" compared with RAID 5. Therefore, the "Write Performance" is very poor. Poor performance and complex implementation methods make raid 6 rarely applied.

At most two disks in the same array can be damaged. After a new disk is changed, the data is recalculated and written to the new disk. According to the design theory, raid 6 must have more than four disks to take effect.

The available capacity is the difference between the total number of hard disks and 2, multiplied by the minimum capacity. The formula is as follows:

\ Begin {Align} size & = (n-2) \ times \ min \ left (S_1, S_2, S_3, \ dots, s_n \ right) \ end {Align}
Similarly, the capacity of the Data Protection Area is multiplied by 2 by the minimum capacity.

Raid 6 is also the most common disk array level in the hardware disk array card function.

Raid 1 + 0 \ RAID 0 + 1

Raid 10 first mirror and then partition the data, and then divide all the hard disks into two groups. It is regarded as the lowest combination of RAID 0, and then the two groups are regarded as RAID 1.

Raid 01 is the opposite of RAID 10 programs. It is to first partition and then mirror the data to two hard disks. It divides all hard disks into two groups and becomes the lowest combination of RAID 1. The two hard disks are regarded as RAID 0.

When one hard disk in raid 10 is damaged, other hard disks will continue to operate. Raid 01 as long as one hard disk is damaged, all hard disks of the same RAID 0 group will stop operating, leaving only the hard disks of other groups to operate, with low reliability. If a raid 01 is created with six hard disks and three RAID 0 instances are used, three hard disks will be taken offline if one hard disk is damaged. Therefore, raid 10 is far more commonly used than RAID 01. Most retail boards support RAID 0/1/5/10, but not raid 01.