Span Depth RAID 10

In the context of RAID (Redundant Array of Independent Disks), "Span Depth" typically refers to a characteristic of certain RAID configurations, especially in RAID levels that involve nesting or combining multiple RAID levels within a single array. The term "Span Depth" is more commonly associated with nested RAID levels, such as RAID 10 (or RAID 1+0).

In RAID 10 (also known as RAID 1+0), data is both mirrored (RAID 1) and striped (RAID 0). Here's how it works and how the "Span Depth" concept applies:

• Mirroring (RAID 1): In RAID 1, data is duplicated across two or more drives. This provides redundancy because if one drive fails, the data can be reconstructed from the mirrored drive(s). The "Depth" in this context refers to the number of mirrored sets in the array. For example, in a RAID 10 configuration with four drives, you might have two mirrored sets (Depth = 2), each consisting of two drives.

• Striping (RAID 0): In RAID 0, data is divided into blocks and distributed across multiple drives for improved performance. There is no redundancy in RAID 0, so if one drive fails, data loss occurs.

• Span Depth in RAID 10: The "Span Depth" in RAID 10 refers to the number of mirrored sets (RAID 1) within the array. It determines how many drives are used for mirroring data. The total number of drives in the RAID 10 array is typically an even number and should be divisible by the Span Depth. Each mirrored set contributes to redundancy, but the array can still sustain one or more drive failures without data loss, depending on the configuration.

For example, in a RAID 10 array with eight drives (4 pairs of mirrored sets), the Span Depth would be 4. Each set of two drives is mirrored, and the data is striped across these mirrored sets for improved performance. This configuration provides redundancy for up to four drive failures (one drive from each mirrored pair).

The Span Depth value depends on your specific RAID configuration goals and the number of drives available. It's essential to choose an appropriate Span Depth based on your needs for performance, redundancy, and the number of drives you have at your disposal. Different Span Depths can result in varying levels of redundancy and performance, so it's important to balance these factors according to your specific use case and available hardware.