RAID 1

D.

The RAID (Redundant Array of Independent Disks) is a storage technology that combines multiple physical hard drives into one logical unit to provide fault tolerance, increased performance, or both.

Among the different RAID levels, there are two main categories: mirroring (also known as RAID 1) and striping (also known as RAID 0).

• Mirroring duplicates the data across two or more disks, so that if one disk fails, the other(s) can still function as a backup. However, it does not improve performance.
• Striping divides the data across two or more disks, allowing data to be read or written in parallel, thus increasing performance. However, it does not provide redundancy.

There are also hybrid RAID levels that combine both mirroring and striping to provide both performance and fault tolerance. The most common ones are:

• RAID 0+1 (also known as RAID 01): it first stripes the data across multiple disks (RAID 0), and then mirrors the striped set to another set of disks (RAID 1). This provides both high performance and fault tolerance, but requires at least four disks.
• RAID 10 (also known as RAID 1+0): it first mirrors the data across two or more pairs of disks (RAID 1), and then stripes the mirrored sets (RAID 0). This also provides both high performance and fault tolerance, but requires at least four disks.

In the case of the question, the correct answer is D, RAID 10. RAID 10 performs mirroring first, then striping. This means that it duplicates the data across multiple pairs of disks, and then divides the duplicated sets across the remaining disks. For example, in a four-disk RAID 10 array, the data would be mirrored across two pairs of disks, and then the two mirrored sets would be striped across the remaining disks.

RAID 1 only performs mirroring, RAID 0+1 performs striping first and then mirroring, and RAID 6 performs double parity for fault tolerance.