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RAID Redundant Array of Independent Disks

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RAID (Redundant Array of Independent Disks) is a technology used to improve data storage performance, reliability, and capacity by combining multiple physical disk drives into a single logical unit. The goal of RAID is to provide redundancy, fault tolerance, and/or increased performance depending on the RAID level implemented.

There are several RAID levels, each with its own characteristics and benefits. Let's go through the most commonly used ones:

  1. RAID 0 (Striping): RAID 0 improves storage performance by striping data across multiple drives. It splits data into small blocks and distributes them evenly across the drives, allowing for parallel read and write operations. This results in increased data transfer rates and overall performance. However, RAID 0 does not provide any redundancy or fault tolerance. If one drive fails, all the data stored across the entire array may be lost.
  2. RAID 1 (Mirroring): RAID 1 provides data redundancy by mirroring the contents of one drive onto another. Every write operation is performed on both drives simultaneously, ensuring that both contain identical copies of the data. If one drive fails, the system can continue to operate using the surviving drive without any data loss. RAID 1 provides excellent fault tolerance, but it doesn't offer increased storage capacity or performance improvement.
  3. RAID 5 (Striping with Parity): RAID 5 combines striping and parity to achieve both improved performance and fault tolerance. Data is striped across multiple drives like in RAID 0, but the parity information is also distributed across the drives. Parity is a calculated value used to reconstruct data in case of a drive failure. RAID 5 requires a minimum of three drives, and the parity information allows for the recovery of data if any single drive fails. RAID 5 provides increased storage capacity, good performance, and fault tolerance.
  4. RAID 6 (Striping with Double Parity): RAID 6 is similar to RAID 5, but it uses two parity blocks instead of one. This provides additional fault tolerance, allowing for the recovery of data even if two drives fail simultaneously. RAID 6 requires a minimum of four drives and offers higher fault tolerance than RAID 5. However, it has a higher overhead due to the additional parity calculations, resulting in slightly reduced performance compared to RAID 5.
  5. RAID 10 (Mirrored Striping): RAID 10 combines the features of RAID 1 and RAID 0. It requires a minimum of four drives and creates mirrored pairs of drives (RAID 1), and then stripes the data across these pairs (RAID 0). RAID 10 provides excellent fault tolerance and performance. It can sustain multiple drive failures as long as they don't occur in the same mirrored pair. However, RAID 10 has the highest overhead among the commonly used RAID levels since it requires a large number of drives.

Other RAID levels, such as RAID 2, 3, 4, and 7, exist but are less commonly used in practice.

Overall, RAID offers improved performance, fault tolerance, or a combination of both. The selection of a specific RAID level depends on the desired balance between performance, capacity, and fault tolerance requirements of a particular storage system.