I think the ansers are too complex. evolve60 did not provide enough information, but as he said "upgrading my HDD to a newer 1tb WD HDD", so it doesn't means mirror the old HDD with the new one, if he does this, he can only use part of the disk space and still face to the low disk space problem.
To uprade the HDD, you can copy the entire old disk to the new one, easeus partition master can help you copy and resize the partitions at the same time.
To mirror the new disks, you can use hardware raid or software raid. If hardware raid, you need to config the raid array firstly, and then copy the old HDD to this raid virtual disk. If software raid, you need to copy the disk firstly, and then convert basic disk to dynamic in disk management, and mirror with another dynamic disk.
You need not to reformat or reinstall the OS. just copy the HDD.
copy instruction
http://www.partition-tool.com/ease [...] k-copy.htm
It is very useful for the people who want to upgrade HDD.