This looks like an oversight: both FileAppender and RollingFileAppender support the bufferedIO=true/false option, but where FileAppender has a configurable buffer size, RollingFileAppender does not.
A similar issue with RollingRandomAccessFileAppender was addressed in
|Status||Open [ 1 ]||In Progress [ 3 ]|
|Status||In Progress [ 3 ]||Resolved [ 5 ]|
|Resolution||Fixed [ 1 ]|
|Status||Resolved [ 5 ]||Closed [ 6 ]|