w, {Number/String, > -1 || ‘majority’ || tag name} the write concern for the operation where < 1 is no acknowledgement of write and w >= 1, w = ‘majority’ or tag acknowledges the write
-1 = don’t even report network errors0 = default, don’t call getLastError by default1 = basic, call getLastError, but don’t wait for slaves2+= wait for slaves
