Shulou(Shulou.com)06/02 Report--

Question1: what is RAID? What is it made of?

The Chinese name of RAID is redundant array of disks. As the name implies, it is made up of arrays of disks. Therefore, the RAID needs at least two hard drives. The basic idea of RAID is to combine several cheap small disks into a disk group to achieve or exceed the performance of a large and expensive disk.

The early RAID was born not for the security of data, but to improve the reading and writing speed of the hard disk. RAID 0 and RAID 1 are defined for this purpose.

Question 2: what situations require the use of RAID?

As network administrators, we should adopt different types of RAID for the server according to the actual situation. At present, the most popular one is RAID 0Grand raid 1GRO raid 5. Among them, too much RAID1 and RAID 5 are used to ensure the security of data, to the maximum extent to prevent the accidental failure of the disk and the loss of data. On the other hand, RAID 0 is designed to improve the speed of disk reading, and it does not provide any data backup and guarantee functions. Knowing the situation of different RAID applications, we can choose according to the actual situation.

Of course, it will be convenient for those who need to keep a large amount of data on their hard drives to use RAID technology. It is mainly shown in the following aspects-

(1) the speed is enhanced and the server can read data from multiple hard drives at the same time.

(2) the storage capacity is expanded, and more space is made up of multiple hard disks to provide to the server.

(3) the disk can be recovered efficiently. RAID provides high data redundancy, and we can ensure the integrity of the data.

Question3: what are the types of RAID? I hope it can be described in an intuitive and easy-to-understand language.

I'm afraid many articles have introduced the types of RAID, so I won't elaborate on the theory here. Coincidentally, the author saw a picture describing all levels of RAID in foreign countries. I feel that the definition is very accurate in many places, and the effect of RAID will be more significant by looking at the picture. (figure 1)

(1) first explain the first small picture, that is, the water dispenser marked with standalone, which is mainly through the real example of mineral water buckets to provide water for the drinking fountain to compare the differences between the various types of RAID. The outlet holes of the two drinking fountains are equivalent to the interface for reading data, and the water in the mineral bucket is valuable data. These data are read by the user through the data interface of the outlet hole, and the corresponding mineral water corresponds to a hard disk.

Under normal circumstances, our computers (such as home computers rather than servers) have only one hard drive, and this mineral bucket provides the water we need to drink (read the hard disk data). (figure 2)

(2) next look at the second small picture, that is, the one marked cluster. (figure 3) the so-called cluster means cluster, which is a combination of multiple servers into one, and all servers provide the same services and data. As shown in the figure, there are two drinking fountains, indicating that there are two servers, both of which can provide user data (water sources). Users can get the data from the water dispenser on the left or the water dispenser on the right, which virtually provides the user with the efficiency of obtaining water (data). But this kind of cluster cluster has a disadvantage, that is, it needs the hardware support of multiple servers, which causes waste to a certain extent. Generally speaking, it is impossible for small and medium-sized enterprises to allow multiple servers to provide the same data and services.

(3) the third small picture marks Hot swap (figure 4), which means heat exchange. Conceptually, it is a bit like hot backup. That is, a water fountain (server), as in the first picture, it has a hard drive and produces the same amount of water as standalone. However, when there is a problem with the mineral water bucket on the water dispenser, such as the water is gone or the bucket is broken, the heat exchange technology is immediately adopted and the nearby mineral water bucket is put on the water cooler instead of the one with the problem, so as to continue to provide services. But this approach also has a drawback, which requires a bucket for backup and is only useful if there is something wrong with the original bucket. In addition, the bucket change process takes time, which virtually affects the provision of services.

(4) the fourth picture is the boss in RAID, it is said here that he is the boss because he is the earliest RAID. Level 0, or RAID level 0, commonly referred to as band, is a specific performance that makes use of band data mapping techniques. That is, when the data is written to the disk group, it is divided into strips and staggered to write to the disk of the disk group. This brings high Iamp O performance, low overhead, but does not provide any redundancy. The storage capacity of the disk group is equal to the sum of the total disk capacity. (figure 5)

When there is something wrong with either of the two buckets on the water cooler, the user cannot get valuable data (water source) through the outlet, so he does not provide redundancy. Of course, in the process of obtaining water, users get it through two mineral water buckets at the same time, which naturally has an advantage over using only one bucket in many aspects such as water output. Improving the speed of data reading and writing is the most important feature of RAID 0.

Tips:

Some readers may ask if there is something wrong with the top bucket in the RAID 0 diagram, can it also come out of the water? In fact, this diagram is only convenient for everyone to remember and understand RAID, and it is impossible to accurately reflect the types of RAID that can only be explained by theoretical description through a simple diagram. Therefore, we should not be too rigid in the process of understanding the picture.

(5) the fifth figure is also commonly used in RAID. Level 1 is RAID level 1, which is often mentioned as mirror RAID. (figure 6) compared with other levels of RAID, this level takes longer to use. RAID 1 provides data redundancy by writing the same data to each disk of the disk group and "mirroring" it to each disk. Mirroring has always been popular because of its simple implementation and high credibility of the data.

Level 1 processes two or more disks in parallel during read data operations, so the data transfer rate is high, but other operations can not provide a high-speed Icano transfer rate.

Level 1 provides very good data with high credibility and improves the performance of read data operations, but it is very expensive. It is required that the specifications of the disks that make up the disk group are the same, while the capacity of the disk group is only equal to that of one disk.

As shown in the picture, there are two mineral water buckets on the drinking fountain, so that when one of them goes wrong, such as damage or lack of water, it will not affect users' use of mineral water, because the other bucket will provide water intact. Of course, since there is no expansion of the outlet, the amount of water is the same as using a mineral bucket. So there is no change in the effluent speed, but the addition of an extra bucket makes RAID 1 provide maximum redundancy, but does not improve the read speed.

Tips:

There is a detail that requires your readers to pay special attention to. In the picture of RAID 1, two mineral water buckets share a common water outlet, and the natural water output remains unchanged. RAID 5 below is different. I will explain it in more detail later.

(6) the sixth figure is the most commonly used RAID level for servers, that is, RAID 5. (figure 7) the server purchased by my company, whether it is DELL or IBM or dawning server, uses this most commonly used RAID type. This level of RAID is by distributing parity to some or all of the disks in the disk group, and level 5 often uses buffering techniques to reduce performance asymmetry. If the disks that make up the disk group are of the same specification, the capacity of the disk group is equal to the total capacity of the disk, minus the capacity of one disk.

It is mentioned above that RAID 1 only uses a water supply outlet and does not improve the effluent speed. However, in RAID 5, we will find that the three mineral buckets in figure 7 are installed in three water intakes, so that we can provide water for users by three buckets at the same time, and naturally the water outlet speed has been greatly improved. Similarly, it does not matter if there is a problem with one of the three mineral water buckets and will not affect the source of drinking water.

Tips:

There are two points that are not shown in the picture. Here is another illustration to facilitate the reader to have a clear understanding.

(1) only three buckets are shown in figure 7. In fact, as long as we have more than three hard drives (buckets), we can configure RAID5 in real work. There is no problem with four, five or more hard drives to configure RAID 5.

(2) if there is a problem with more than two hard drives after we configure RAID 5, the data can not be effectively protected. In other words, RAID 5 can only keep the data intact if something goes wrong with one of the hard drives.

(3) the last diagram is actually a combination of RAID 0 and RAID 1 introduced above. As long as you have a clear understanding of RAID 0 and RAID 1, this diagram is much easier to understand. In fact, it is configured as RAID 0 and then RAID 1, giving full play to all the advantages of RAID 0 and 1, and avoiding all their disadvantages. In view of the lack of space, we will not go into detail here, after all, there are not as many opportunities to use RAID 0room1 in actual work as RAID 5 described above.

Summary:

For readers who are not familiar with the server, mastering the concept of RAID is the most basic. He is a stepping stone to our entry into the field of server knowledge. I hope the drinking machine diagram in this article will help you understand the various RAID and data redundancy categories. Finally, I would like to reiterate that the picture is only for everyone to understand and remember, many details and characteristics of RAID theory can not be shown through a simple picture, the picture description is incomplete, please forgive me, after all, this article is written for those RAID knowledge laymen's readers.

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