I am using Asus UEFI M5A97 motherboard. I have GPT formatted WD30EZRX Caviar Green 3T. The OS is Win7 64-bit Ultimate. The system is working fine with that hd. I have another hd WD2002FAEX, a Western Digitial 2T Black edition. On it, there is also similar OS Win7 64-bit Ultimate. This one is formatted in normal MBR. It is also working fine on its own.
The problem arise when I am attaching both the hds on the system. I want to boot on the 3T and to treat the 2T as secondary (slave). When I do that the system does not boot. So far I am not able to configure the BIOS to make it work. After a few trying with the BIOS settings, the system manages to boot on the 2T but that is not what I wanted.
The only way I could use all the hd is by 'brute-forth'. I think that's the term. I make use of hds hot swapable. Leave the side cover open at all times. Plug the power cables to all available hds (but not the sata cables - the cables are plugged onto the board only). Plug the sata cable to the 3T drive and boot the system. When the system is up, plug the other sata cable to the other hd that I want to use as secondary. Plug in more sata cables to other hds if you need. I tried with four and the system recognizes them all.
Thank you Mr Mcnumpty23 for confirming sata has no master/slave.
Pressing F8 is equivalent to pressing DEL key to get to selecting the drive to boot as you said. Pressing DEL key also get to a graphical boot menu where we can make Sata Configuration, select Hard Drive BBS Priorities and select Boot Options etc. I suppose that is where I am stuck.
When I select the harrdisk by name, the system hung at POST, unless I select Windows Boot Manager as first boot, and as I said earlier I cannot attach more than one harddisk, system hung at POST.