Windows on a hardware raid array larger than 2TB
Windows can not be installed using GPT on a Legacy system, which includes all of our HP lineup up to and including the 8th generation of HP ProLiant servers. The reason for this limitation is because these servers do not support UEFI, and Windows can only boot from GPT using UEFI mode.
As the alternative to GPT, MBR is only able to support partitioning up to 2TB, certain measurements will need to be taken to allow you to complete the installation.
This problem can be circumvented by creating a smaller RAID array just for the Operating System, which has to be no larger than 2TB, and dedicating the rest of the storage for other partitions (which may be bigger than 2TB).