Thanks for reply. As a matter of fact, I had already taken my own risk and go ahead without overseeing by an expert eye, which had been proved not a good approach!
I did not have the problem you mentioned, because the two disks actually have been partitioned before (exactly the same partition I want except the type is not "0xfd" but "0x83"). I changed the type and go ahead with the creation of RAID. The system did not complain.
The RAID & LVM creation seems fine untill the last step,
#e2fsadm /dev/RAID/Home -L +150G
It gave error message:
# e2fsadm --size +150G LogicalVolumePath
# e2fsadm -- new size too large for "LogicalVolumePath"
# e2fsadm -- size of "LogicalVolumePath" would be invalid
I guess this is a typical newbie error who did not read the howto carefully enough. I already did the LV extention and then e2fsadm will try to do that again. By google search, I understood my mistake and everything is settled now.