The onboard ports are not likely limited to 750 (again, outdated docs) - its limit should also be 2TB (no RAID).  I don't think the SC1430 has onboard RAID (CERC SATA 2s), but if it does, 1TB is the largest. You are right, a SAS interface can also take SATA drives.  On the SAS 5, they cannot be mixed though - all SAS or all SATA.   The SAS 5 supports only RAID 0, 1, and JBOD (non-RAID), so the only way to use 16 disks is in non-RAID mode or in a RAID 0 (no redundancy). The SAS 5 supports a maximum PHYSICAL disk size of 2TB. The SAS 5 supports only 2 virtual disks (arrays). The SAS 5 supports a maximum VIRTUAL disk size of 2TB, which means that with 2TB disks, your ONLY option is RAID 1 (or non-RAID).  Likewise, with 1.5TB disks, a RAID 1 is your only option. Basically, your 6TB VD is not an option.  With 4x1.5TB disks on the SAS 5, you could do 1) two 2x1.5TB RAID 1's, or 2) 4x1.5TB disks in non-RAID mode - these will all show as individual disks in Windows, which would be the same as attaching each drive to the onboard SATA ports (in non-RAID mode, if that is an option).
Hello In the 1430sc specs its stated that a maximum of 4x750 GB disks can be used. Spec sheet. Is this limitation still valid? Recommended parts & upgrades suggests 1 TB disks. I'm aming at 4x1,5=6 TB disks. Is this possible? Best regards /Erik
Disk size in PowerEdge 1430sc