If you start with one drive, and it is in the left bay, it will be Volume 1. And when you add the second drive it will become Volume 2 and the right drive will become Volume 1.

At this point, when the user accesses Volume 1, it will appear as if all of the information is gone, but it´s actually on Volume 2.

If you switch the physical position of the first drive to the Right bay, you will be able to access the files.

The reason this happens is:

There are logical volumes and physical volumes.

A physical volume refers to the actual hard drive.
A logical volume refers to a formatted partition.

• In Standard mode with one disk , the physical volume is irrelevant and the logical volume is Volume 1 regardless of which bay the drive is in.
   
• In Standard mode with two disks, the physical location of the disks will determine which volume is which drive. Volume 1 is always on the right and Volume 2 is always on the left.