I'm currently buying a server that NEEDS 30TB of storage, 15TB of which is logical and 15TB is physical. However the towers only allow 8 2TB 3.5 inch HDD's, which gets me to 16TB. How do I get another box of HDD's without needing another processor? Or does the 16TB fit the 15 logical and 15 physical requirement? I'm having a hard time understanding this.
I think you're confusing a couple things here. Logical memory refers to how Windows allocates memory space. Paging (also known as virtual memory) refers to how Windows will swap memory to disk in order to continue to do calculations in RAM. And then you have your actual disks and storage.
Like Chris states in his comment, logical disks refers to having many disks in a RAID that is presented as one drive to the system. So you could have 15 disks presented as one "drive" for data.
I'm not sure that the MD3000 that ST8 posted will work for you because even though it has 15 bays, it's divided into two managed partitions that as far as I remember can't be bridged. They're handled on two different RAID controllers. EDIT On further reflection, I could be remembering the MD1000. In either case, you need to be sure you can present one contiguous 30TB drive to whichever OS you're using.
Some links to keep you entertained regarding logical memory and paging.
Essentially you'll need to find some kind of external storage, whether DAS or NAS and attach it to your server. As I don't know the requirements of your application, I can't really help you with that. You may want to get a consultant or talk with the sales reps or whomever you have that can support this on site.
Then dont get towers. I am always surprised how people try to fit something large into equipment totally not made for this.
SuperMicro has nice cages for storage computers and JBOD - JBOD has more drives but no place for a motherboard, slave them by SAS chaining. This is up to 80 (!) 2.5" drives in 4he, loaded front and back. Stoage Pod (look it up on google) fits 60 3.5" drives into 4 HE.
it is not that hard to find equipment that totally outsizes your meager requirements. just use google properly. It will not e a rack of te mill tower, though.
THAT SAID - I know of a maxi tower there you can fit 6 2.5" cabinets each with 8 discs. That is 48tb raw capacity ;)
I'd suggest getting a server with a minimal hard drives to support the OS and attaching a raid array to it. An MD3000 for example