128 volumes is the default mode for SAS RAID controller, the 16 volumes mode is used for support roaming this raidset to SATA RAID controllers. The SATA RAID controller is designed to support upto 16 volumes only. You have to use "Max 16 volumes" on the raidset mode if you plan to roam this raidset between SAS RAID controller and SATA RAID controller.
Tags: BIOS, raidset, SAS, SATA