The minimum number of drives required for RAID 10 is four. RAID 10 disk drives are a combination of RAID 1 and RAID 0, the first step of which is to create a number of RAID 1 volumes by mirroring two drives together (RAID 1). The second step involves creating a stripe set with these mirrored pairs (RAID 0). In its original form this was called RAID 1+0, but has been abbreviated to RAID 10. If you had any less than four drives you would only be able to make a single RAID 1 mirror set.
RAID 10 should not be confused with RAID 0+1, which involves creating two RAID 0 stripe sets and then mirroring them. They have very similar characteristics and use the same number of drives, but are not the same.
Related Q&A from Steve Pinder
When adding an old hard drive to RAID sets on servers, it’s important to account for factors such as the number of drive bays in the host. See how to...continue reading
In this Ask the Expert, Steve Pinder talks about which RAID level to choose, depending on the criticality of your data or the capacity required.continue reading
Learn about the differences between a FATA disk and a Fibre Channel drive, and find out how to determine which drive type is better for Exchange 2007...continue reading