RAID arrays with different size disk units?

Are there any circumstances where disk units of a different size can be added
to an existing RAID array?  The Backup and Recovery manual states that you
need 4 disk units of the same size to start RAID protection, and that
additional units can be added later.  But it is unclear whether these need to
be the same size units.

I currently have one RAID array that isn't full; it has four 2gb drives (raw
size).  Can I add 4gb (or larger) disk units into this array?  We have added
disk units into an existing array in the past, but they have always been of
the same size.

If this can be done, what is the resulting usable size of the new units?  In
the above case, establishing RAID protection ended up leaving us with four
units of 1475mb each.  (I.E., 25% was used on each of the four units).  

Scott Lindstrom
Zenith Electronics Corp
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