nosort in index creation

are there any disadvantages using nosort in creating an index

The only disadvantage I can think of is the following:

You use NOSORTwith index creation on realy huge table. You are certain that rows are placed in database blocks in a sorted order, however there is a row back there at the end of the table that realy is not in the right place, it should be somewhere else for the whole table to be realy sorted. So your index creation runs runs for two hours when Oracle finds the offending row and abort the index creation. So you have just lost two hours of your's and computer's time, that's the disadvantage.

wow that sucks. real time wasted. Is there any way to find out if the rows are in sorted order before doing this?

Not that I'm aware of.