what is a raid configuration

Redundant Array of Independent Disks (RAID)

A data storage virtualization technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both. Data is distributed across the drives in one of several ways, referred to as "RAID levels," depending on the level of redundancy and performance required.

Common RAID Levels

  • RAID 0 (Striping): Divides data evenly across two or more disks, with no redundancy. Improves performance but offers no fault tolerance. Failure of any drive results in complete data loss.
  • RAID 1 (Mirroring): Duplicates data onto two or more disks. Provides excellent data redundancy, as the system can continue operating if one drive fails. Read performance may improve, but write performance is typically limited by the slowest drive.
  • RAID 5 (Striping with Parity): Distributes data and parity information across three or more disks. Offers a balance of data redundancy and performance. Can tolerate the failure of one drive. Write performance can be slower than RAID 0 due to parity calculations.
  • RAID 6 (Striping with Dual Parity): Similar to RAID 5 but includes two sets of parity data distributed across the disks. Can tolerate the failure of two drives. Offers higher data protection than RAID 5 at the cost of slightly reduced write performance.
  • RAID 10 (RAID 1+0): Combines mirroring (RAID 1) and striping (RAID 0). Requires a minimum of four disks. Provides both high performance and high redundancy.

Key Concepts

  • Parity: A calculated value used to reconstruct data if one of the drives fails in a RAID level that uses parity.
  • Striping: Dividing data into blocks and distributing those blocks across multiple drives.
  • Mirroring: Creating an exact copy of the data on multiple drives.
  • Redundancy: The ability of the system to continue operating even if one or more drives fail.

Implementation Methods

  • Hardware: Utilizes a dedicated RAID controller card to manage the RAID array. Typically offers better performance and features than software implementations.
  • Software: Uses the host operating system's resources to manage the RAID array. More flexible but often less performant than hardware RAID.
  • Firmware/BIOS-based: Implemented in the system's firmware, offering a middle ground between hardware and software solutions. Performance and features may vary.

Considerations

  • Capacity: The usable storage space depends on the level and the number of disks used. Some levels, like RAID 1, significantly reduce the usable capacity.
  • Performance: Different levels offer different performance characteristics. Striping improves read/write speeds, while parity calculations can impact write performance.
  • Data Recovery: While improves data protection, it is not a substitute for backups. If multiple drive failures occur beyond the level's tolerance, data loss can still happen.
  • Cost: The number of disks required and the complexity of the controller can affect the overall cost.