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How to understand Raid technology, in view of this problem, this article introduces the corresponding analysis and answer in detail, hoping to help more partners who want to solve this problem to find a more simple and feasible method.

Redundant array of independent hard disk (RAID, Redundant Array of Independent Disks), formerly known as redundant array of cheap disks, referred to as hard disk array. The basic idea is to combine several relatively cheap hard drives into a hard disk array group, so that the performance can reach or even exceed an expensive hard disk with huge capacity. Depending on the version selected, RAID has one or more of the following benefits over a single hard drive: enhanced data integration, enhanced fault tolerance, and increased processing capacity or capacity. In addition, to a computer, a disk array looks like a separate hard disk or logical storage unit.

To put it simply, RAID combines multiple physical hard disks into a single logical disk, so the operating system only treats a raid array as a single hard disk. RAID is often used on server computers and often uses exactly the same hard disk as a combination. Due to the falling price of hard drives and the more efficient integration of RAID functions with the motherboard, it has also become a choice for players, especially for jobs that require a lot of storage space.

The initial RAID is divided into different levels, each of which has its own theoretical advantages and disadvantages. Different levels strike a balance between the two goals, namely, increasing data reliability and increasing memory (group) read and write performance. The common RAID level is RAID-0,RAID-1,RAID-5,RAID-6,RAID-10,RAID-50,RAID-60.

Introduction to RAID at various levels RAID0

Merge multiple disks into one large disk, without redundancy, parallel IcanPot O, the fastest. RAID 0 is also called band set. It is a juxtaposition of multiple disks to form a large disk. When storing data, it segments the data according to the number of disks, and then writes the data to those disks at the same time, so RAID 0 is the fastest of all levels. However, RAID 0 has no redundancy, and if a disk is (physically) damaged, all data will be lost, which is as dangerous as JBOD.

In theory, more disk performance is equal to "single disk performance" × "disk count", but in practice, RAID performance decreases with margin due to the bottleneck of bus Ibino and other factors, that is to say, suppose the performance of one disk is 50MB per second, the RAID 0 performance of two disks is about 96MB per second, and the RAID 0 of three disks may be 130MB per second instead of 150MB per second. Available capacity is the total number of hard drives multiplied by the minimum capacity of a single hard disk: Size= (N) * min (S1Magic S2memS3. SN)

RAID1

RAID1 is a RAID disk array made up of two hard drives, whose capacity is only equal to the capacity of one hard disk, because the other is just "mirrored" as data. The RAID 1 disk array is clearly the most reliable array because it always maintains a complete backup of the data. Its performance is naturally not as good as that of the RAID 0 disk array, but it does read data faster than a single hard drive because the data is read from the faster of the two hard drives. The write speed of the RAID 1 disk array is usually slow because the data has to be written to two hard drives and compared. The RAID 1 disk array generally supports "hot swapping", which means that the removal or replacement of hard drives in the array can be carried out while the system is running without interruption. The RAID 1 disk array is very secure, but it is also a more expensive RAID disk array solution because two hard drives can only provide the capacity of one hard disk. RAID 1 disk arrays are mainly used in situations where data security is high and corrupted data is required to be recovered quickly.

RAID5

RAID Level 5 is a storage solution that combines storage performance, data security and storage costs. It uses Disk Striping technology. RAID5 needs at least three hard disks. Instead of backing up the stored data, RAID5 stores the data and the corresponding parity information on each disk that makes up the RAID5, and the parity information and the corresponding data are stored on different disks respectively. When one of the disk data of RAID5 is damaged, the remaining data and the corresponding parity information can be used to recover the damaged data. RAID 5 can be understood as a compromise between RAID 0 and RAID 1. RAID 5 can provide data security for the system, but the degree of protection is lower than that of mirrors, and the utilization of disk space is higher than mirrors. RAID 5 has a data read speed similar to that of RAID 0, only because of the addition of parity information, the speed of writing data is slightly slower than that of writing to a separate hard disk, and the use of "write-back cache" can improve performance a lot. At the same time, because multiple data correspond to a parity information, the disk space utilization of RAID 5 is higher than that of RAID 1, and the storage cost is relatively cheap.

The available capacity is the difference between the total number of hard drives minus 1, multiplied by the minimum capacity of a single hard disk, and the formula is Size= (NMel 1) * min (S1Magens S2Magi S3. SN).

RAID6

Compared with RAID 5, RAID 6 adds a second independent parity block. Two independent parity systems use different algorithms, and the reliability of the data is so high that even if two disks fail at the same time, it will not affect the use of the data. However, RAID 6 needs to allocate more disk space for parity information, which has a greater "write loss" than RAID 5, so the "write performance" is very poor. Because of its poor performance and complex implementation, RAID 6 is rarely used in practice.

A maximum of two disks are allowed to be damaged in the same array. After the new disk is replaced, the data will be recalculated and written to the new disk. According to 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 drives minus 2, multiplied by the minimum capacity of a single hard disk, and the formula is Size= (NMel 2) * min (S1Magens S2Mages S3. SN).

RAID10

The combination of RAID 1 and RAID 0, first RAID 1, then RAID 0, that is, multiple groups of RAID 1 form Stripe access to each other. Because RAID 10 is based on RAID 1, and RAID 1 requires at least 2 hard drives, at least 4 hard drives are required to form RAID 10 with multiple sets of RAID 1. Taking the configuration of the smallest four hard drives of RAID 10 as an example, we first divide the four hard drives into two groups, and each group of two hard drives constitute RAID 1, so we get two groups of RAID 1, and then the two groups of RAID 1 form RAID 0.

The RAID10 remains operational when one of the underlying RAID 1 drives is damaged, but if two hard drives in either group of RAID1 are damaged, the entire set of RAID10 fails.

RAID 10 because there are several groups of RAID 1 in the upper layer to form Stripe, the capacity utilization rate is 50%. For example, the total capacity of raid10 made by 4 hard drives is the capacity of two hard drives.

RAID50

The combination of RAID 5 and RAID 0, first RAID 5, then RAID 0, that is, multiple groups of RAID 5 form Stripe access to each other. Because RAID 50 is based on RAID 5, and RAID 5 requires at least 3 hard drives, at least 6 hard drives are required to form RAID 50 with multiple sets of RAID 5. Taking the configuration of six hard drives with the smallest RAID 50 as an example, six hard drives are divided into two groups, and three in each group constitute RAID 5, so two groups of RAID 5 are obtained, and then two groups of RAID 5 are formed into RAID 0.

The RAID 50 will remain operational if one hard drive in any one or more groups of RAID 5 is damaged, but if two or more hard drives in any group of RAID 5 are damaged, the entire RAID 50 will fail.

RAID 50 has higher performance than simple RAID5 and lower capacity utilization than RAID5 due to the composition of several groups of RAID5 into Stripe in the upper layer. For example, for the same 9 hard drives, RAID 50 is composed of 3 RAID 5 RAID 0, each RAID 5 will lose one hard disk capacity, utilization is (1-3), RAID 5 is (1-1).

RAID60

The combination of RAID 6 and RAID 0: first RAID 6, then RAID 0. In other words, Stripe access to more than two groups of RAID 6. RAID 6 requires at least 4 hard drives, so the minimum requirement for RAID 60 is 8 hard drives.

Because the underlying layer is made up of RAID 6, RAID 60 can allow up to 2 hard drives to be damaged in any group of RAID 6, while the system can still operate; however, as long as 3 hard drives in any set of RAID 6 are damaged, the whole set of RAID 60 will fail, of course, the probability of this is quite low.

Compared with simple RAID 6, the upper layer of raid 60 combines multiple groups of RAID 6 to form Stripe access, so the performance is higher. However, the high threshold for use and low capacity utilization is a big problem.

RAID level comparison

The answers to the technical questions on how to understand Raid are shared here. I hope the above content can be of some help to you. If you still have a lot of doubts to be solved, you can follow the industry information channel to learn more about it.

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