I have a client who are attempting to create a six disk RAID 10 array on the SBI-7126T-S6 blades, however, under "SAS Topology" we can see all six drives, but as soon as they go to "Create a RAID" only four drives are displayed.
The LSI 2008 controller reports firmware 15.00.00.00-IR
You can try update LSI firmware as following link.
https://www.supermicro.com/wdl/driver/SAS/LSI/2008/IR_IT/Firmware/IR/