So here's a question from an almost complete novice on all this: If I can RAID the three other 500Gb drives in my MP simply using disk utility, can I make a RAID 1 using that RAID and an external 1Tb drive? Can you RAID a RAID? Or would it just need to be a Time Machine b/u of that internal RAID?
Even if Disk Utility allowed this, I wouldn't try it. RAID 1 volumes must be equal sizes, so it would only be able to use 1 TB of your three 500 GB drives, in order to match the 1 TB external drive. Also, write speeds would be limited by the single external drive.
And incidentally, what's the point of buying a RAID card for a RAID 0 or 1?
The cache on the card might provide a slight speed-up, but probable not noticeably. Unlike with software RAID, it is possible to install firmware updates while booted from a hardware RAID set. The RAID card will allow the use of SAS drives. Unless you need RAID 5, or SAS drives, there is no reason to buy the RAID card.
I bought this 2007 MP used with the Apple RAID card in it and those three drives set up as a RAID 0. Why was the card necessary?
It wasn't, unless the previous onwer was thinking of RAID 5. You can remove the card if you want to, and regain deep sleep capability. Just read the card installation manual backwards. Make sure you have good backups, since you will probably lose all the data when setting up software RAID.
<http://manuals.info.apple.com/en
US/MacPro_RAIDCardInstallation.pdf>