Redundant Array of Independent Disks (RAID) is a technology used in data storage systems to improve data availability, fault tolerance, and performance. It involves combining multiple physical disk drives into a single logical unit to achieve better reliability and performance than a single disk alone.

RAID works by distributing data across multiple drives in different ways, depending on the specific RAID level or configuration. Each RAID level offers a different combination of performance, fault tolerance, and capacity. Here are some commonly used RAID levels:

1. RAID 0 (Striping) :
   * Data is evenly distributed across multiple drives without redundancy.
   * Offers improved read and write performance as data can be accessed from multiple drives simultaneously.
   * No fault tolerance - if one drive fails, the entire array is affected, potentially leading to data loss.

2. RAID 1 (Mirroring) :
   * Data is mirrored between pairs of drives.
   * Provides data redundancy - if one drive fails, data is still accessible from the mirrored drive.
   * Read performance may be improved, but write performance is typically not enhanced.
   * Requires twice the storage capacity as data is duplicated on each drive. 3. RAID 5 (Block-Level Striping with Parity) :
   * Data is striped across multiple drives, and parity information is distributed across all drives.
   * Provides fault tolerance - if one drive fails, the data can be reconstructed using parity information and data from the remaining drives.
   * Offers good read performance and decent write performance.
   * Requires a minimum of three drives.

4. RAID 6 (Block-Level Striping with Double Parity) :
   * Similar to RAID 5, but with an additional parity drive for enhanced fault tolerance.
   * Can tolerate the failure of two drives simultaneously.
   * Provides better data protection and fault tolerance than RAID 5, but at the cost of reduced write performance.
   * Requires a minimum of four drives.

There are additional RAID levels, such as RAID 10 (a combination of RAID 1 and RAID 0), RAID 50 (a combination of RAID 5 and RAID 0), and RAID 60 (a combination of RAID 6 and RAID 0), which offer various trade-offs between performance, capacity, and fault tolerance.