VRAID-1 means that data is stored on two different physical disk drives. The EVA *always* binds two disk drives together as a 'pair' which it uses to store VRAID-1 data, even when you don't use any virtual disks with VRAID-1.
If one disk of such a pair fails, the EVA takes the data from the surviving disk and copies it to a new pair of disks, provided that the disk group has enough free space.
There are no dedicated spare disk drives, so the EVA needs to reserve enough space within the disk group. Setting the so-called "protection level" (which only reserves space for reconstructing redundany, but does not protect the data itself) to single (or the value 1) means the EVA will reserve space that calcultes by: 2 times the size of the largest disk in the disk group.
.
