I've not used DiskPart. I use FDISK. When I did the home desktop machine, I couldn't find FDISK on the Win 7 DVD so I used Knoppix (Linux run from a CD) which was as easy as shelling peas. It has two programmes that will do the job - GPartEd or QTPartEd - just to be sure.
There are now three hard drives in that machine, partitioned from C to L, with two external USB ones for backup (M and S). S is up in the attic where burglarisationers can't get to it.