Data storage reliability is one of the mostimportant and current issues in computer systems. Therefore, a lot of efforts and developments were concentrated in this direction, and as a result, there appeared a technology for constructing RAID-arrays, which, despite the fact that it was invented several years ago, is quite relevant and in demand at this time.
Let's try to figure out what it istechnology. To get started is to give a definition of the main term. So, a RAID array is a kind of redundant set of independent disks that serve to increase the fault tolerance and efficiency of computer systems. The first is achieved precisely because of redundancy, and the second is due to the simultaneous operation of disks that are in the created array. It is worth noting that the RAID system is used as a single disk by the system due to the interaction of software and hardware.
To answer the question of how to createRAID, it is necessary to mention that there are several different variations (levels), the implementation of which depends on the organization of the work of disks. The overall operation of the disks can be organized using either parallel or independent access. In the first case, for recording information, disk space is divided into strips (blocks), which then fall into different physical disks (performance improves due to simultaneous recording of strips). When reading information, all operations are also performed in blocks, which contributes to an even greater increase in the efficiency of such a system. Moreover, the more drives, the more productive the RAID will be. But there are some nuances. It is impossible to organize such a system if the block size is larger than the size of the request for recording information itself.
In case of independent access all informationA separate user request is recorded in the same way as when working with one logical disk, but unlike the latter situation, when reading, operations will already be performed on different (separate) disks.
At the moment there are severalstandard methods of organization (levels) of a system such as a RAID array. They are numbered from 0 to 6 and are called, respectively, RAID 0, RAID 1, and so on. In practice, the most commonly used levels are: 0, 1, 3, as well as 5.
So, to practically implement the externalRAID, you need to have two components: a RAID controller that performs the functions of distributing incoming information, communicating with the main server, generating redundant data, and any array of hard drives. This is the so-called hardware option for creating a RAID array. But this is not the only way to organize disks. The construction of such a system is possible from the so-called software environment. In this embodiment, the creation of RAID arrays carried out using special tools that are supported by one or another operating system. The disadvantage of this implementation is that if a PC software fails, all information stored on logical RAID disks will be lost. In addition, we must remember that it is programmatically possible to build an array of only the first and zero levels.
