Redundant Array of Inexpensive Disks (RAID)
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Redundant Array of Inexpensive Disks (RAID)
RAID (Redundant Array of Independent Disks) is a concept in storage subsystems that offers a higher level of protection against downtime and data loss compared to traditional disk drives. RAID refers to a drive architecture that utilizes redundancy to protect critical data. In theory, RAID arrays, composed of traditional disks, can operate for hundreds or even thousands of years without data loss in the event of a disk failure. RAID also provides other benefits: it can enhance input/output performance, simplify and accelerate maintenance, and allow users to fine-tune the drive system according to the specific needs of a particular application.
The RAID concept was first introduced by researchers at Berkeley in 1987. Their work defined five levels of RAID: five methods for distributing data across multiple disks to prevent data loss due to a single disk failure. Among the initial designs, three levels proved to be commercially attractive: Level 1, Level 3, and Level 5. Although not strictly considered RAID, an additional level, Level 0, is often included in RAID designs because its design is similar to the original ones.
Level 0 distributes data across disks through striping, a technique that stores consecutive data blocks on different disks. Striping improves I/O throughput but provides the same data protection as traditional drives. Level 1 achieves data redundancy through mirroring, which saves the same data on two different disks. Mirroring provides excellent reliability and some improvement in I/O throughput, but is relatively inefficient in terms of disk capacity usage.
Level 3 and Level 5 combine striping and parity codes to recover data in case of disk failure. Both Level 3 and Level 5 use disk capacity more efficiently than Level 1. RAID is not just about redundancy. RAID helps with automatic load balancing, avoiding hotspot disks where 80% of I/O requests are directed to 20% of disk capacity. Choosing the right RAID level can accelerate data transfer or handle more I/O requests per second. Level-3 hard drives quickly process large amounts of data by transmitting data from all disks in parallel, reducing the transfer time for applications such as image processing or CAD when reading large continuous files. Level-5 arrays can handle a large number of I/O requests simultaneously, making them ideal for applications that generate many small requests.