I looked up the 1863 Griffiths Valuation head of household listing for Clonallan civil parish. There were three Peter Berry entries and one Peter Barry entry. Assuming your ancestor was still living in 1863, he is likely one of those four records.
I also looked on Roots Ireland and there are baptismal records for Berry and Barry children where the father was Peter but in all situations the mother's name was Mary Campbell.
Roger McDonnell
Roger McDonnell
http://www.failteromhat.com/griffiths/down/clonallan.htm