how many drives needed for raid
RAID 10: How many disk drives should you use? 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.
Maximum number of drives in RAID 1 can be 32, from a starting number of 2(even number of disks are required.) Striping and parity are not used in RAID 1 You can refer the diagram shown in mirroring of raid section in this article, for RAID 1.