ASROCK 775DUAL-880PRO Manual To Installation And Configuration page 12

Create JBOD
The data on disk drives will be destroyed if user uses "Auto
Setup" to create a JBOD. However, you can reserve the data on
the first disk drive of a JBOD array if you use "Select Disk
Drives" to select disk drives
The data on the first disk drive will be reserved and the other disk
drives in JBOD will be expanded behind the first disk drive and
become free space.
Expand Span (JBOD) Array function is not available if VT8237
only supports 2 SATA ports.