"In fact, there's a problem that just arise: the virtual drive has its partition
table in MBR instead of GPT, that prevents large partitions.
I did not have the option while configuring the OS in the service CD ;
was it because I selected the size of the system partition to be only
300GB ? My plan was to create the "data" partition of ~5,7TB after installation. "
When you installing an OS the system will automatically select MBR partition if you not choose different partition table (which is not allowing large partition, 4 Gb maximum or less ).
The best way is to checked if the hardware system sustain processor - EFI ( Extensible Firmware Interface) for being able select the GPT partition table.
If you instaled already the OS and want to beneficiate of EFI advantages and GPT table then you need to reinstall the OS again because you need to choose EFI mode before this.
Otherwise the system automatically will use MBR partition table.
Also I recommend to create two virtual drives, one to be just with the OS and the other for data in redundancy and safety purpose.
Please see bellow the steps which are involving activating EFI - GPT partition table
1) Configure RAID group in LEGACY mode
2) In BIOS change boot type in EFI
3) Reinstall OS - Windows Server 2012 - choose the hard drive and you will need to mount RAID card driver and the just click on the bellow link for the RAID drivers.
XXXXXXXXX RAID CARD DRIVERS XXXXXXXXXXXXXXXXXXX
4) Reboot server – press F11 – select EFI USB dispositive – then follow the wizard steps.