if you are upgrading to 8g it may not work. my system would only recognize a mismatched 4g and 2g for 6g. even the 2g boost from 4g made some speed improvement
on my install i had to initialize the drive in a ext case on another system. if you are going to install new os from a usb (ubuntu, osx) almost any format will do that assigns partition and a system type. then the system will recognize that the drive is there and permit loading of a system. that may work with a recovery drive as well. after the quick format i tested both my osx and my ubuntu usb loaders. system found both of them.