Nested RAID Levels: Understanding RAID 10 and Beyond

Nested RAID levels (also called hybrid RAID) combine two or more standard RAID levels to improve performance, redundancy, or both by layering their properties.

RAID 10 (or RAID 1+0) is a common nested RAID configuration that first creates multiple RAID 1 (mirroring) arrays and then stripes (RAID 0) across those mirrored sets. This means data is mirrored for redundancy and then striped for performance, combining the strengths of both RAID 1 and RAID 0. Specifically, RAID 10 mirrors pairs of drives and then stripes data across these mirrored pairs, enhancing fault tolerance and read/write speeds.

Key points about RAID 10 and nested RAID levels:

• The order of numbers matters: RAID 10 (1+0) mirrors first, then stripes; RAID 01 (0+1) stripes first, then mirrors. This affects fault tolerance and rebuild complexity.
• Nested RAID levels like RAID 10, RAID 50 (striping over RAID 5), and RAID 60 (striping over RAID 6) are designed to balance performance and redundancy beyond what single RAID levels can offer.
• RAID 10 requires a minimum of four drives and offers high performance and fault tolerance but at the cost of usable storage capacity (about 50% of total raw capacity).
• Other nested RAID configurations include RAID 0+1, RAID 5+0, and RAID 10+0, each combining different RAID levels to optimize for specific needs.

In summary, RAID 10 is a nested RAID level combining mirroring and striping to deliver both high performance and redundancy, making it popular in environments requiring fast, reliable storage. Nested RAID levels extend this concept by layering RAID types to tailor performance and fault tolerance characteristics beyond standard RAID levels.