Friday, April 6, 2012

What is RAID 0?

RAID 0 is called Stripe or Striping. It stands for the highest memory function of all RAID. RAID improves memory property by scattering continuous data to several disks for access. Then data request can be concurrently executed by several disks and every disk only executes the data request belonging to it. This kind of data concurrent operation can sufficiently apply the Bus bandwidth and dramatically improve the memory property of whole disk.

Brief Introductions to RAID 0
RAID 0 is not real RAID structure and it has no data redundancy. RAID continuously segments data and concurrently read and write in several disks, so its data transmission rate is very high. However, data reliability is not provided while the property is improved. And one disk failure will influence the whole data. Therefore, RAID 0 must not be applied when high data availability is needed. 

RAID is the abbreviation of redundant Array of Independent Disks. It is a redundant array composed of several disks. Although containing several disks, RAID is an independent large storage device in operating system. The main advantages of applying RAID in memory system are following.

  1. Providing across function by combing several disks into a logical volume;

  2. Improving disk access speed by deviding data into block and concurrent reading and writing on several disks;

  3. Providing Fault Tolerant function through mirror image or program check run
The initial purpose of RAID was to save costs. The total price of several small capacity disks was lower than the price of large capacity disk at that time. Its cost saving is not obvious for now. But the advantages of several disks have been shown sufficiently by RAID. Its speed and throughput are much better than that of any single disk. Besides, RAID provides excellent Fault Tolerant function. It keeps on working even there is something wrong with any single disk and the destroyed disk has no influence on it.

RAID technologies are divided into several levels providing different speeds, securities and cost performance. According to reality of situation, suitable RAID level is adopted to meet user's requirement for availability, property and capacity of memory system. Common RAID levels include NRAID, JBOD, RAID0, RAID1, RAId0+1, RAID3, RAID. Among them, RAID 5and RAID(0+1) are used frequently.

The Working Principle of RAID 0
As shown in the figure, system sends out 3 I/O data requests to RAID disks array composed of 3 disks) and these data requests are transfered into 3 operations. And each operation is corresponding to one physical disk. The pictures clearly show that sequential data requests are scattered into 3 disks and executed concurrently. Theoretically, the concurrent operations of 3disks triple disk read-write speed at one time. But the actual speed must be lower than theoretical speed because of influences from Bus Bandwidth and other aspects. However, compared with serial transmission, parallel transmission of mass data has remarkably developed the speed. 

Advantages and Disadvantages of RAID 0
One disadvantage of RAID 0 is that is does not provide data redundancy. Once data corruption occurs, the damaged data can not be recovered. During the operation of RAID, that any single disk goes wrong will influence the whole data. Thereby, it is not recommended for enterprise users. The features of RAID 0 are suitable for users who need higher performance but lower data security in work areas such as graphic workstation. For individual users, RAID 0 is the best choice to improve hard disk storage performance.

Disk Array of RAID 0
RAID 0 has no striping of disk array for Default Tolerant.
1. Both disks of RAID0 must have the same size and capacity.
2. When the primary and standby disk allocation is changed, both disks of RAID 0 must be rezoned, and all data in disk will be lost. The positions of the two disks in the same tracks can be changed in the condition of not changing the primary and standby disk allocation and it has no influence on data read-write operation in disk.
3. When disks composed of RAID 0 are changed into non-RAID mode or a couple of non-RAID disks are changed into RAID 0 mode, system will redivides the corresponding disks and all data in the disk will be lost. 

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