There are different types of RAID, or configurations if you like, and what it sounds like you did was set up disk mirroring. So there's an identical copy of data on both drives. What you wanted is called RAID 0 (technically it's not RAID, since the R stands for Redundant) or disk spanning. That probably would require reinstalling the OS, so you probably didn't see it as an option if one of the drives is a boot drive.
Generally speaking RAID 0 is a bad idea. One drive goes down, the data on both is inaccessible. There is absolutely no fault tolerance (which is the whole point of RAID) in that config.
<span id="INSERTION_MARKER">I tried
to convert two 80 Gig external hard drives into a 160 Gig hard drive using Disk
Utility's RAID function. <span>
<div><span>Surprise, I can only store 73 Gig on the RAID. That's
of no value.??</div><span>
<div><span>Either I have done something wrong (Don't understand the RAID
function) or I have to split the RAID back into two 80 Gig hard drives again.</div><span>
<div><span>??I
tried to restore the two drives and gave up after letting my Mac Mini run for
over 24 hours.??
<span>
<div><span> Help
</div></div>

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