The IBM System Storage DS3500 series storage subsystems support up to two redundant RAID controllers in either a 12 or 24 drive configuration. The models for the storage servers are DS3512 and DS3524. There are also two models of drive expansion chassis, a 12 LFF and a 24 SFF drive version, that can be attached to either of the storage subsystems. The models for these are EXP3512 and EXP3524.An important difference between the DS3512 and the DS3524 product models and their equivalent expansion models are the hard disks that are supported with them. The difference starts with the physical drive size and extends to their speeds and storage capacities. The DS3512 and EXP3512 support 12 drives in the 3.5 inch format; the DS3524 and EXP3524 supports 24 drives in the 2.5 inch format. The disk drives are installed at the front, as shown in the below figures.IBM Storage Manager v10.86 or greater, inconjuntion with Controller FW v7.86, is required to enable the HDD capable T10 PI funtionality.