Data Center RAID and Storage

RAID (Redundant Array of Independent Disks) provides data redundancy and performance improvements by combining multiple physical drives. Here is how to accurately calculate RAID capacities and understand their speeds.

In the formulas below, N is the total number of drives in the array and S is the capacity of a single drive.

RAID Levels Overview

• RAID 0 (Striping):

  • Capacity: N * S
  • Speed: Excellent read/write performance.
  • Trade-off: No redundancy. If one drive fails, the entire array is lost. Requires minimum 2 drives.

• RAID 1 (Mirroring):

  • Capacity: S
  • Speed: Very good read speed, write speed equivalent to a single drive.
  • Trade-off: High cost (50% usable capacity) for 1 drive redundancy. Requires minimum 2 drives.

• RAID 5 (Striping with Distributed Parity):

  • Capacity: (N - 1) * S
  • Speed: Good read speed, but suffers from a “write penalty” due to parity calculation.
  • Trade-off: Efficient capacity usage with 1 drive failure tolerance, but slow rebuild times. Requires minimum 3 drives.

• RAID 6 (Striping with Double Parity):

  • Capacity: (N - 2) * S
  • Speed: Slower writes than RAID 5 (calculates two parities).
  • Trade-off: Can survive 2 simultaneous drive failures. Requires minimum 4 drives.

• RAID 10 (Striped Mirrors):

  • Capacity: (N / 2) * S
  • Speed: Excellent read and write performance (no parity calculations).
  • Trade-off: Lower capacity efficiency (50% usable). Safely tolerates 1 drive failure per mirrored pair. Requires minimum 4 drives.

Remember, RAID is for uptime and hardware fault tolerance; it is not a backup!