RAID Disk Array
Although RAID with multiple hard drives, but the operating system as a stand-alone large-scale storage devices. The use of RAID technology in storage system benefits mainly in the following three ways: in the early stages of computer development, “high capacity” hard drive prices are quite high, to solve the problem of data storage security main method is to use the backup tape machines and other equipment, which Although the kinds of methods can guarantee the security of data, but access and backup jobs are quite tedious.
In 1987, Patterson, Gibson, and Katz the three University of California, Berkeley engineers delivered a speech entitled “A Case of Redundant Array of Inexpensive Disks (Redundant Array of Inexpensive Disks program),” paper, the basic idea is to more than just capacity of smaller, relatively inexpensive hard drive organic combination of its performance more than one big expensive hard drive.
The design idea was soon accepted, from RAID technology is widely used, data storage into faster, more secure, more affordable new era.
Disk Array for PC users, it is quite strange and mysterious. Impression of the disk array seem to stay in such a scenario: In the spacious hall, lined with the disk cabinet, several expressions gloomy, bald engineer early wandering, in which constantly out of a block from a heavy hard drive, and then Insert a block seems to be more heavy hard drive … … finally, with the large capacity hard drives continue to lower the price of personal computers continue to improve the performance, IDE-RAID disk performance improvements as the cheapest solution, started to enter the ordinary user’s computer system .
By combining multiple disks grouped together to provide the disk as a logical volume across functions;
By the data into multiple data blocks (Block) parallel write / read multiple disks to increase disk access speed;
By mirroring or parity operation to provide fault tolerance;
The main purpose of the initial development of RAID is to save costs, then the price of a few small-capacity hard drive to be less than the sum of large-capacity hard drive. Now look at RAID in the role of cost-saving is not obvious, but the RAID can fully play the advantages of multi-block drive to achieve far beyond any one single hard drive speed and throughput. In addition to performance improvements in addition, RAID can also provide a good fault tolerance, in any one case of hard drive problems can continue to work hard the impact will not be damaged.
RAID technology is divided into several different grades, respectively, to provide different speeds, safety and cost-effective. Based on the actual situation of selecting the appropriate RAID level to meet the users of storage system availability, performance and capacity requirements. Commonly used RAID levels are the following: NRAID, JBOD, RAID0, RAID1, RAID0 +1, RAID3, RAID5, etc.. Now regularly using RAID5 and RAID (0 +1).
RAID (Disk Array) is a hard disk drive controller to control the number of mutual connections, so that multiple hard drive read and write synchronization, reduce errors, increase efficiency and reliability technology. Disk array card is the realization of this technology hardware products, disk array card has a dedicated processor, also has a dedicated memory used to cache data. Server using the disk array card directly through the operation of the disk array card processing, so do not need a lot of CPU and system memory resources, not reduce the disk subsystem performance. Array card dedicated processing unit to carry out operations, its performance is much higher than that of conventional non-array of hard drives, and more secure and stable.
RAID technology, two main characteristics: first, speed second, it is safe, because these two advantages, RAID technology has been applied to the early high-level server SCSI interface hard disk system, with the development of computer technology in recent years, PC machine CPU has entered the era of the speed of GHz. IDE interface hard disk to be outdone, have launched a ATA66 and ATA100 hard drive. This makes RAID technology has been applied to middle and low personal PC, or even possible. RAID is usually caused by a hard disk in the RAID array tower controller or RAID card in the computer achieved. RAID is a Redundant Array of Inexpensive Disks English acronym, the Chinese referred to as Redundant Array of Inexpensive Disks. Simply put, RAID is a multi-block into a separate hard drive (physical disk) by combining in different ways to form a disk group (logical drives), which provides higher storage than a single hard disk performance and providing data backup technology. The different ways the composition of the disk array as RAID levels (RAID Levels). Data backup function is user data in the event of damage, the use of the backup information can allow corrupted data to be restored, thus protecting the user’s data security. The user appears to form a disk group is like a hard drive, users can partition it, format and so on. In short, the operation of disk arrays with a single hard drive exactly the same. The difference is that the disk array storage rate is much higher than a single hard disk, and can provide automatic data backup.
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