I would say neither solution is more secure than the other.
Potentially the 2 drive config be more secure as a potential thief has to steal two drives instead of one, but that's hardly a security measure. That's also assuming that they dont just leg it with the whole PC.
Im sorry if I have mislead you guys. I want to make sure my data is secure from a crash. I am under the impression that if I install one 1.5 Tb drive and partition it as OS partition and Data partition, if one partition crashes do I lose all the info on the drive. Hence my thought of using 2 seperate drives.
The only way for a HDD to "crash" is if it physically fails somehow. If the drive stops working, all the partitions on it will also fail.
What your referring to is redundancy, not security. There are ways to make a redundant storage system, mainly through RAID arrays.
The partition idea has no redundancy, if the drive fails everything goes down.
With the dual drive system mentioned above you have don't really have any redundancy. You have two drives, but both have equal chances of failing and one is vital to the machine working.
However, if you were to go into a RAID1 configuration on two identical drives for your boot drive, it reduces your chance of total drive failure by half.