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Rading hard drives
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Server manufacturers connect hard drives to ensure that data is adequately protected and can be quickly accessed. Computer engineers call such an arrangement a 5 redundant array of inexpensive disks (RAID). By arranging drives in sets, users hope to take advantage of the higher seek times of smaller drives. A special hard disk controller, called a RAID controller, ensures that the RAID array's individual drives are seen by the computer as one large disk drive.
RAID schemes are numbered, with higher numbers indicating more elaborate is methods for ensuring data integrity and fault tolerance (or a computer's ability to recover from hardware errors).
| Raid 0 | Raid1 | Raid2-4 | Raid5 | |
| Fault tolerance? | No | Yes | Yes | Yes |
| What does it do? | Called disk striping, RAID 0 breaks data into blocks that are spread across all drives rather than filling one before writing to the next. | Called disk mirroring, RAID 1 uses two identical drives: data written to the first is duplicated on the second. | RAID 2-4 are rarely used and simply enhance the striping provided by other RAID levels. | Called striping with parity, the popular RAID 5 writes error- correcting, or parity, data across available drives. |
| What are the advantages? | Improved disk I/O throughput - the fastest of all RAID configurations as it distributes read/write operations across multiple drives. | Good for imaging and scientific work where speed is important. If either drive fails, the other continues to provide What are the advantages? uninterrupted access to data. | 2 enhances 0 by using additional drives to store parity data. 3 enhances 2 by requiring only one error-checking drive. 4 build son 3 by using larger block sizes, boosting performance. | If one drive fails, its contents are recovered by analysing the data on the remaining disks and comparing it with the parity data |
| What are the disadvantages? | The failure of any single drive means the entire array is lost | Inefficient use of disk space. | Uses dedicated disks to store the parity data used to reconstruct drive contents. Up to 30% more hard disk space needed than 1. | Not as fast as RAID 0. |
Дата публикования: 2015-03-29; Прочитано: 1314 | Нарушение авторского права страницы | Мы поможем в написании вашей работы!
