OK, that changes the complection of things a bit...
You state:
Dabullz said:
My original H/D... <snip> ...needs to be erased and reformatted.
May I ask why? From what I understand of your posts, that doesn't sound like a bad idea at all, especially if you do a
completely clean install of your OS and all the apps. But (and it's a biggie) that's a fairly major job to be undertaking. To avoid data-loss, you need to be
absolutely certain that you have a
thorough backup of every app's data-files in a safe location. It sounds a bit like you're fairly well on the way to achieving that with the data you have on your iTunes drive -however, double and
triple-check you have
everything before you start reinstalling your OS.
Now, would I be right in assuming that at this point you are yet to reformat the iTunes drive, so it still has a copy of the OS and apps on there? If so, no biggie... I would however personally be inclined to transfer just the data-files that you need to retain to a drive that has nothing on it, then reformat that (iTunes) drive. That will avoid inadvertently picking-up the detritus of unnecessary files, consuming space and adding the potential or confusion down the track.
We're still a fair way from rearranging your data to suit just yet -bear with me.
Once that is done, we're about ready to turn your Mac Pro into an inglorious "dumb box"!!!
First, my thinking: From what I know of your system, you have an original drive of 750GB, named Macintosh HD. You also have two additional drives (of undefined size, but we'll assume more than adequate) for storage, one of which is named iTunes, the other let's say named Photos. Straight away that gives us a pretty darn good idea of what is going to go where. Let's work towards that.
That Macintosh HD is
definitely the drive for your OS, apps, documents, spreadsheets, emails and sundry bits of digital life -there is a shed-load of room on that drive to do everything you'll require for some considerable time to come. I wouldn't even consider putting it anywhere else. So do a clean reinstall of your OS and apps there. There's little need for any decision-making on your part at this point. The installation process will take care of directing all the software to the (new, empty) data files on your system.
Once that is done, you'll have the basics of your system set-up complete.
The data that you have backed-up on one of your drives now needs to be re-placed in the appropriate locations so that your software can find it. From there, pretty much all you need to do is put all the media files that the iTunes app will handle on your iTunes drive and all your photos (or whatever you decide) onto your photos drive, then tell the appropriate apps where to look!
Once you've done that, you'll have acres of room across all those drives for future expansion.
Dabullz said:
... does the OSX recognize them as one giant drive?
Nope, OS-X will see and you will have three separate and distinct volumes.
Dabullz said:
My experience with nearly full drives is that they don't function very well...
Quite correct -
absolutely in the case particularly of your "main" (Macintosh HD) drive, where your OS and apps live.
Now, someone else will be able to advise you correctly here (my lack of OS-X knowledge precludes me being certain), there may be a way for you to copy the contents of your user home folder (prior to doing the format/reinstall of OS-X) to another drive and then replace it after the reinstallation to protect data like your contacts, email, calendars etc... I'm pretty sure there is, so best you get the correct information before proceeding.
All the best!