Disk array (diskette array) principle

Why do I need a disk array? How to increase the speed of disk access (acces), how to prevent data loss due to disk failure and how to effectively use disk space, has been a computer professionals and users worry, while the high cost of large-capacity disk, the user form a great burden. The generation of disk array technology solves these problems.

Over the past decade, CPU processing speeds have been almost geometrically accelerated, and memory (memory) Access has increased dramatically, while data storage devices, which are disks (hard disk), have a faster access rate. More slowly. The entire i/0 throughput can not match the system, forming the bottleneck of computer system, reducing the overall performance of the computer system (throughout) if the disk can not be effectively improved access speed, CPU, memory and disk imbalance will make the CPU and memory improvements to form a waste.

There are two main ways to improve disk access speed at present. One is disk cache controller, which has cache memory to reduce the number of disk accesses from disk-read data. Read and write data in the cache memory, a significant increase in the speed of access, such as the data to be read is not in cache memory, or to write data to disk, to do the disk access action. This approach is under a single duration environment (single-tasking envioronment) such as DOS. Access to a large amount of data has good performance (small and frequent access is not). However, it is not possible to display performance under a multitasking (multi-tasking) environment (because of the movement of data exchange (swapping) or database access (because each record is small). There is no security in this way.

One is the use of disk array technology. A disk array is an array of multiple disks, used as a single disk, it stores data in a segmented (striping) way on different disks, and when data is accessed, the associated disks in the array act together: significantly reducing data access time and better space utilization. The different technologies used by the disk array, called RAID level, different level for different systems and applications to solve the problem of data security.

Generally high-performance disk arrays are sufficient for the form of hardware to achieve, in-step to the disk cache control and disk array combination of-a controller (RAID controler) or control card, for the same users to solve the disk output/into the four requirements of the system:

(1) Increase the access speed.

(2) Fault tolerance (fault tolerance), that is, security.

(3) Effective use of disk space.

(4) Try to balance the CPU, memory and disk performance and different, improve the overall performance of the computer.

Disk array principle

In 1987, a member of the University of California, Berkeley, published a paper entitled "Disk Array Research", formally referring to the raid is the array of AIDS, the paper proposed a cheap 5. 25 "and 3. The 5 "hard drive can also be a 8" disk on a large machine that delivers human capacity, high performance, and data consistency, and details the Raidl to 5 technology. The different technologies used by the disk array for different applications, called RAID Level,raid, are abbreviations for the redundant Array of inexpenslve disks, while each level represents a technology that is currently recognized by the industry as RAID0-RAID5. This level and a representation of the high and low, level5 is not higher than Level3,level1 also a lower than level4. Words to sample what kind of RAID level products, pure depending on the user's operating environment (operating envir0nment) and application (application), and level of the high and low has no inevitable relationship. RAID0 no security, only its rapid, so suitable for high-speed i/0 system, raidl suitable for security and speed of the system, RAID2 and RAID3 for large computers and images, CAD/CAM processing, etc. RAID5 for 0LTP, due to the more than the financial institutions and The urgent need of large data processing centers, so the use of more and more famous, but also formed a lot of people to the disk array misunderstanding, that the disk array must be RAID5, RAID4 less use, and RAID5 have their common, but RAID4 suitable for large amounts of data access. Others such as Raid6,raid7. Even RAIDl0, 50, 100 and so on, are manufacturers to do their own, and there is no consistent standard, this does not explain.