On the page http://api.mongodb.com/java/current/com/mongodb/WriteConcern.html

w

0: Don't wait for acknowledgement from the server
1: Wait for acknowledgement, but don't wait for secondaries to replicate
>=2: Wait for one or more secondaries to also acknowledge
"majority": Wait for a majority of secondaries to also acknowledge
"<tag set name>": Wait for one or more secondaries to also acknowledge based on a tag set name

majority - should specify majority of data-bearing nodes, not secondaries, since majority with a PSS replica set only needs data written to one secondary