Understanding RAID Levels: Performance, Redundancy, and When to Use Each

RAID 0

RAID 0 can use two or more hard drives or SSDs to improve read performance by striping data across the drives in blocks (typically 64 KB). The controller writes the first block to disk 1, the second to disk 2, the third to disk 3, then cycles back, providing combined capacity and theoretically up to three‑times faster reads.

However, if any disk fails, all data is lost, and the more disks used, the higher the failure probability, so frequent backups are essential.

RAID 1

RAID 1 creates an exact mirror of data on two separate disks, providing redundancy: if disk A fails, disk B still contains all data. Mirroring is not a backup; deleting a file on one disk deletes it on the other. Frequent backups remain necessary.

Read performance is similar to a single disk, while write performance is slower because data must be written to both disks simultaneously.

RAID 10 and RAID 01

RAID 10 (or 1+0) mirrors data first (RAID 1) and then stripes it (RAID 0); RAID 01 (0+1) stripes first then mirrors. Both require at least four disks. RAID 10 offers better fault tolerance because a single disk failure does not compromise the mirrored sets, whereas RAID 01 can lose the entire array if a disk fails during the striping stage.

RAID 3

RAID 3 uses one dedicated parity disk and the remaining N‑1 disks operate like RAID 0. If a data disk fails, the parity information can reconstruct the lost data. However, every read/write operation involves all disks, and the parity disk itself is a single point of failure.

RAID 5 and RAID 6

RAID 5 distributes both data and parity blocks across all disks, allowing the array to survive a single disk failure. Read performance scales with the number of disks, but write performance suffers due to parity calculation.

RAID 6 adds a second parity block (Q) to RAID 5, enabling the array to tolerate two simultaneous disk failures. Recovery uses both P and Q parity calculations.

RAID 50 and RAID 60

RAID 50 combines multiple RAID 5 groups with a RAID 0 stripe, improving write performance over RAID 5 while retaining good read speed. It requires at least six disks.

RAID 60 combines multiple RAID 6 groups with a RAID 0 stripe, offering higher fault tolerance (surviving two disk failures per sub‑group) at the cost of additional disks (minimum eight).

Conclusion

In terms of read capability: RAID 5 ≈ RAID 6 ≈ RAID 60 > RAID 0 ≈ RAID 10 > RAID 3 ≈ RAID 1.

In terms of write capability: RAID 10 > RAID 50 > RAID 1 > RAID 3 > RAID 5 ≈ RAID 6 ≈ RAID 60.