raid controller data transfer rate

Solution 1:

That particular RAID controller claims 8-lane PCI Express 2.0 compliancy meaning that effectively you'll already be limited to 8 * 4 Gbs = 32 Gbs (or 4000 MB/s) regardless of what's connected to the RAID card.

Each SAS SFF8088 connector will cary 4 SAS lanes over a single cable, when each link is at the maximum 6 Gbs port speed theoretically you indeed get 2 x 4 x 6 Gbs = 48 Gbs worth of bandwidth that the RAID controller can manage.

A 6 Gbs SAS link will be shared by the number of devices connected to it, so if you connect 4 devices and each is stressed equally you can only get 1,5 Gbs per individual drive.

Solution 2:

Based on my experience with similar controllers like Smart Array P420i from ProLiant ML350p Gen8 or ServeRAID M5015 SAS/SATA Controller from IBM x3560 M3 I'd say: 6Gbps per mini-SAS (i.e. 12Gbps) - best possible scenario. I have not tested two SFF8088 ports, only one, and I've hit 6 gbps limit.