Asus PCI-DA2200 - Manual (Page 298)

ASUS GUI RAID Manager: Array Management
4.16 Dynamic Logical Drive Expansion 4-47
The screen will display that volume set of Drive E: has
been extended by the 900MB in Disk2. Move the cursor to
"Commit Changes Now" to confirm that you want the free
space to become a part of the same logical drive.