The Ultra-10 was originally designed in 1997 and first shipped to customers in 1998.
The Ultra-10's onboard IDE chipset doesn't have
the capabilities for [url=http://www.48bitlba.com/]48bit addressing[/url].
That's all you're going to get out that system.
You can choose to "waste" the rest of the disk(s) or you can choose
to use IDE drives that are smaller than that limitation, such as a 120GB disk.
Additionally, there are no aftermarket adapters cards
compatible with the system's SPARC architecture.
Such cards may work in a PeeCee, but not in your Sun system.