What is the MINIMUM number of disks needed for a RAID 10 array?

A RAID 10 configuration, also known as RAID 1+0, combines the features of both RAID 1 (mirroring) and RAID 0 (striping). To create a RAID 10 array, data is first mirrored across pairs of disks, and then the striped data is spread across multiple mirror sets.

The minimum requirement for a RAID 10 array is four disks. This is because, in order to implement both mirroring and striping effectively, there need to be at least two sets of mirrored disks (each consisting of a pair). Each pair of disks is exactly mirrored, so you need two pairs to form the basis of the stripe.

In simpler terms, with only two disks, you wouldn't achieve both mirroring and striping since RAID 1 requires a minimum of two disks for mirroring alone, and RAID 0 cannot operate without at least two disks for striping. Therefore, four disks are necessary to satisfy the requirements of both RAID configurations within RAID 10.