When changing the RAID mode from "Big" to "Safe100", the drive may report the wrong capacity. There are three steps to fix the problem.
The procedure below will solve the problem on Macintosh computers running OS X
IMPORTANT NOTE: Following the procedure below will ERASE ALL DATA on the drive. Prior to following these directions, verify important data is stored securely on a different storage device.
Switch the disk to JBOD mode. This change will allow each disk to be seen separately. Start the repartition process on each drive.
Begin by opening Disk Utility. This program is found in Applications, then in the Utilities folder. In the walkthrough below, we will be fixing a 20GB hard disk. All computers will look slightly different.
The disk is listed on the left side. Click the entry that says the size (18.6GB in this case.) Choose the Partition tab along the top.
Change settings to match the example. Volume Scheme should say 1 Partition, and Format should say Mac OS Extended (journaled)
Click the Options button.
From the following list, set the appropriate option for the computer the drive will connect to.
Click OK when the proper option is selected. Doing so will return the display to the Disk Utility window. Click Apply.
In fewer than 30 seconds, the drive will be reformatted and repartitioned. Repeat this process for the second drive. Once each has been partitioned and formatted separately, switch the disk back to safe 100 mode. The disk should now show the proper capacity. Perform the process on the single volume that now appears, and the disk is ready for use.